Technical Reference Manual GM-16 Level Switch Models GM-16 & GM-16R Document ID: 31437 Nuclear
Revision history Version Description Date 1.0 Initial release. Was part number 218599. 051201 1.1 Changed company name, logo, and website 110301 Copyright 2011 VEGA Americas, Inc, Cincinnati, Ohio. All rights reserved. This document contains proprietary information of VEGA. It shall not be reproduced in whole or in part, in any form, without the expressed written permission of VEGA Americas, Inc. The material in this document is provided for informational purposes and is subject to change without notice. ISO 9001 approval by Lloyd's Register Quality Assurance Limited, to the following Quality Management System Standards: ISO 9001:2000, ANSI/ASQC Q9001-2000, Approval Certificate No. 107563. VEGA Americas, Inc 4170 Rosslyn Drive Cincinnati, Ohio 45209-1599 USA Voice: +1 513-272-0131 Fax: +1 513-272-0133 Website: www.vega-americas.com Warning: Use this equipment only in the manner that this manual describes. If you do not use the equipment per VEGA specifications, the unit is not CE compliant, and may be damaged or cause personal injury.
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Table of Contents Preface ix Explanation of symbols......................................... ix Your comments............................................. xi Introduction 1-1 Theory of nuclear gauging....................................... 1-1 Benefits of nuclear gauging.................................... 1-2 Applications............................................ 1-3 Radiation collimation........................................ 1-4 Overview of instrument........................................ 1-5 Low level alarm........................................... 1-5 High level alarm.......................................... 1-6 Failsafe alarm........................................... 1-6 Nuclear materials notice........................................ 1-7 Safety................................................. 1-8 General............................................... 1-8 Manufacturer s responsibility.................................... 1-8 User s responsibility........................................ 1-8 Licensing requirements (U.S.A.).................................. 1-9 Customer service........................................... 1-10 U.S. and Canada.......................................... 1-10 Worldwide............................................. 1-10 Have this information ready.................................... 1-10 Installation 2-1 Shipping and transportation...................................... 2-1 Unpacking the equipment....................................... 2-2 Storing the equipment......................................... 2-3 Installation procedures........................................ 2-4 Mounting the equipment........................................ 2-5 Location on vessel......................................... 2-5 Access inside vessel........................................ 2-6 Orientation with other vessels................................... 2-7 Wiring the equipment......................................... 2-8 Interconnect............................................ 2-8 Detector Housing........................................ 2-8 Electronics Housing....................................... 2-9 Jumpers............................................. 2-9 Input and Output.......................................... 2-10 Installation drawings.......................................... 2-11 Operation 3-1 Components of the gauge....................................... 3-1 Radioactive source......................................... 3-1 Source holder........................................... 3-2 Geiger Mueller (GM) detector................................... 3-2 Failsafe Alarm........................................... 3-4 GM-16 and GM-16R Technical Reference Manual iii
Watch Dog Timer.......................................... 3-4 Calibration of gauge.......................................... 3-5 Choosing auto-calibration or manual calibration.......................... 3-5 Auto-calibration......................................... 3-5 Manual calibration....................................... 3-5 Calculations............................................ 3-6 Calibration............................................. 3-7 Operate mode............................................. 3-9 Field intensity........................................... 3-9 Maintenance 4-1 Product specifications......................................... 4-2 Source............................................... 4-2 Source holder........................................... 4-2 Geiger Mueller tube (detector)................................... 4-2 Detector and electronics housing(s)................................ 4-3 Electrical.............................................. 4-3 8032 Microprocessor........................................ 4-4 Auxiliary and/or optional equipment.................................. 4-5 Troubleshooting............................................ 4-6 Process problems......................................... 4-7 GM-16/GM-16R level switch.................................... 4-7 Source/source holder...................................... 4-7 Geiger Mueller tube....................................... 4-8 Auxiliary and/or optional equipment................................ 4-8 Flowcharts............................................. 4-8 Flowchart #1.......................................... 4-9 Repairs................................................ 4-12 Orders............................................... 4-12 Recommended spare parts...................................... 4-13 Ordering spare parts........................................ 4-13 VEGA shop order number....................................... 4-14 Reference Drawings.......................................... 4-16 Glossary 5-1 Index Index-1 -iv GM-16 and GM-16R Technical Reference Manual
List of Figures 1.1 Theory of level of switches............................... 1-2 1.2 Example of a low level alarm............................. 1-5 1.3 Example of a high level alarm............................. 1-6 2.1 Mounting the GM-16 on an isolated vessel...................... 2-6 2.2 Mounting the GM-16 on adjacent vessels....................... 2-7 2.3 D-51683 Outline of the detector s shock mount assembly...............2-12 2.4 D-52057 GM-16 electrical connections........................2-13 2.5 D-52301GM-16R electrical connections........................2-14 2.6 D-52014 GM-16 detector housing with 2 hubs.....................2-15 2.7 D-51855 GM-16 Detector housing with 2 hubs - CENELEC approval.........2-16 2.8 D-52311 Outline of GM-16R detector and electronics housing............2-17 2.9 D-52312 Outline of GM-16R detector and eletronics housings - CENELEC approval.2-18 3.1 How the GM tube works................................ 3-2 3.2 Field intensity versus response time.......................... 3-3 3.3 LEDs.......................................... 3-7 4.1 Troubleshooting flowchart 1 of 3............................ 4-9 4.2 Troubleshooting flowchart 2 of 3............................4-10 4.3 Troubleshooting flowchart 3 of 3............................4-11 4.4 B-52331 GM-16 Parts identification..........................4-17 4.5 C-52351GM-16R Detetector and remote parts identification.............4-18 GM-16 and GM-16R Technical Reference Manual v
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List of Tables P.1 Explanation of symbols................................. ix 1.1 Contact information.................................. 1-10 3.1 Interpretation of green and red LEDs......................... 3-9 3.2 Field Intensity At The Detector............................. 3-10 4.1 Recommended spare parts list for the GM-16/GM-16R................ 4-14 GM-16 and GM-16R Technical Reference Manual vii
viii GM-16 and GM-16R Technical Reference Manual
Chapter 0PREFACE Explanation of symbols Table 0.1 Explanation of symbols In the manual Radiation notice Introduces information concerning radioactive materials or radiation safety. Caution Introduces warnings concerning potential damage to the equipment or bodily harm. On the instrument AC current or voltage A terminal to which or from which an alternating (sine wave) current or voltage may be applied or supplied. DC current or voltage A terminal to which or from which a direct current voltage may be applied or supplied. Potentially hazardous voltages A terminal on which potentially hazardous voltage exists. Protective ground terminal Identifies location of terminal intended for connection to an external conductor. GM-16 and GM-16R Technical Reference Manual ix
Preface NOTES x GM-16 and GM-16R Technical Reference Manual
Preface Your comments Manual: GM-16 and 16-R Level Switch Technical Reference Manual Date: Customer Order Number: Your contact information (optional): Name: Title: Company: Address: Did you find errors in this manual? If so, specify the error and page number. Did you find this manual understandable, usable, and well organized? Please make suggestions for improvement. Was information you needed or would find helpful not in this manual? Please specify. Please send your comments to: VEGA Americas, Inc. Director of Engineering 4241 Allendorf Drive Cincinnati, OH 45209-1599 USA Fax: +1 513-272-0133 equipment. GM-16 and GM-16R Technical Reference Manual xi
Preface xii GM-16 and GM-16R Technical Reference Manual
C HAPTER 1 Chapter 1INTRODUCTION This chapter gives an overview of the measurement system you have purchased and discusses the theory under which it operates. Theory of nuclear gauging A nuclear transmission gauge is designed to measure the density, level, or weight of a process material by directing a beam of gamma radiation energy from a source, through the process material to a detector assembly (sensor & amplifier) on the other side. Some of this energy is absorbed during the passage through the material. This absorption is proportional to the mass of the material through which it passes. The amount of radiation energy which reaches the detector is measured and converted into electrical impulses which are then counted. These counts are sent to a computerized electronic component contained within the gauge. (In the GM-16R, the computerized electronic component is housed separately.) The computerized electronics has the function of converting the raw data into a useful format which can trigger an alarm or be applied directly to the manufacturing process through interaction with a personal computer. This principle is the basis of nuclear instrument measurement. In a point level measurement gauge, such as the GM-16/GM-16R, the gauge detects the absence or presence of a material between the source and the detector and triggers an alarm on the gauge as well as an external, user-supplied, alarm. GM-16 and GM-16R Technical Reference Manual 1-1
Introduction Figure 1.1 Theory of level of switches Benefits of nuclear gauging The following benefits of nuclear gauges are realized when your GM-16/GM-16R is properly installed and utilized: The capability of sensing and controlling process variations with extremely good sensitivity, with no moving parts, and with long term stability from industrially-proven electronics. No contact with the process material itself, thereby reducing maintenance. Outputs from these end instruments, that make the computer control of the process, a reality. VEGA gauging systems are without equal for measurement control of the level of solids and slumes contained in silos, bins, process vessels and pipes. Reliability and accuracy are assured since the non-contact principle eliminates the possibility of fouling, gumming, clogging, or crucial components becoming inoperative. The gauges can provide recording only, recording and simple alarm, or high and low level alarm. 1-2 GM-16 and GM-16R Technical Reference Manual
Introduction Applications VEGA level gauges cover a wide range of applications. The simplest type, and most common, is a single source and single detector used for high or low level detection. (This is a LevelArt 1000 Series gauge.) In a typical arrangement, the GM-16/GM-16R detects the level of liquid in a vessel when it has exceeded a predetermined limit. The level limit is defined by an imaginary straight line drawn from the source to the detector. As an example of a high limit switch, when the feed valve is open, liquid is fed into the vessel and the liquid level rises. The liquid level will rise until it interrupts the radiation beam. There is then a change in the field intensity at the detector due to absorption by the process of some of the energy present in the beam, and the instrument puts out an alarm signal in the form of a relay contact changeover. This signal may be used to close the feed valve or activate an annunciator. As the liquid is used from the vessel, the level will fall, thus again exposing the detector to the radiation beam and the feed valve will be opened when the contacts revert to normal. Conversely, the source and detector may be lowered to below the liquid level and the system functions as a low limit switch in which case the system will produce an alarm when the liquid level falls below this low limit. The liquid itself may be under pressure, at high temperatures, or even corrosive, but its characteristics will not affect the switch since the system components are outside of the vessel. There may be many variations of this system, such as filling a hopper with solid material through a gate. In such a system, depending upon the type of process material, there may be jostling and settling of the material. A hysteresis band about the required level prevents fluttering and spurious alarm situations. Where both a high level and low level indication are desired on a vessel, two detectors are required, one set for high level and one set for low level. When the difference in height between low level and high level is equal to or less than the diameter of the vessel, only one source is required with the two detectors. (This is a LevelArt 1100 Series gauge.) When the difference in height is greater than the diameter of the vessel, two sources are required with the two detectors. (This is a LevelArt 1200 Series gauge.) The LevelArt 1000 Series gauges (single source and single detector) are also used on pipes or chutes to indicate the presence or absence of materials. If the switch is to be located in a well within a bin, or relatively high in an inaccessible location, use of a remote electronics unit is desirable. In such cases, only the GM tube(s) and a single preamplifier are on the vessel, while all the remaining circuits and sensitivity adjustments are remotely located in an accessible location. The remote sensor design is also advantageous in situations where space at the sensor location is a problem. GM-16 and GM-16R Technical Reference Manual 1-3
Introduction Radiation collimation For all practical purposes, radiation can be considered to travel in a straight line. Although it can not be focused with lenses, as light can be, it can be collimated. Within a source holder, a source is surrounded on all sides except one (forward) with lead shielding. This shielding will absorb most of the radiation and bring the radiation field at the outside surface of the gauge to an acceptable level. The radiation which emerges from the front of the source holder will pass through an opening whose shape is carefully formed. In the case of a point level gauge used for either high or low level detection, a single source and single detector are used and the beam is collimated into a circular beam. When both high and low level detection are required and two detectors are used with two sources, then the radiation is also collimated into a circular beam. But, when both high and low level detection are required and two detectors are used with a single source, the radiation is collimated into a fan shape. (Depending on the type of the source holder used, this beam may be collimated up to 45º.) Looking down from the top, the beam is very narrow - it is a fan rather than a cone. 1-4 GM-16 and GM-16R Technical Reference Manual
Introduction Overview of instrument The VEGA Model GM-16/GM-16R Level Switch is an instrument designed to indicate a change in the process material level by sensing a change in radiation field intensity. By placing a source of radiation on one side of a vessel or pipe and a GM-16/GM-16R Level Switch (with Geiger-Mueller detector inside) on the other side, changes in material level are indicated as the level passes above or below the GM-16/GM-16R. When the material level is below the detector, the maximum amount of radiation from the source reaches the detector. When the material level is above the source and detector, only a small amount of radiation reaches the detector due to the fact that the material absorbs much of the radiation energy as it is passing through. The Level Switch can be calibrated to trigger an alarm for either condition: a low level process alarm or a high level process alarm. Low level alarm The low level alarm condition occurs when the radiation field intensity exceeds some calibrated threshold. When the level of a substance in a vessel is above the point at which it is set to alarm, the field intensity will be low. When the level drops below this point, the field intensity increases and the alarm is triggered, indicating that a low level has been attained within the vessel. Figure 1.2 Example of a low level alarm GM-16 and GM-16R Technical Reference Manual 1-5
Introduction High level alarm The high level alarm condition occurs when the radiation field intensity drops below some calibrated threshold. When the level of a substance in a vessel is below the point at which the Level Switch has been set, the field intensity is high. When the substance level passes this point, the field intensity drops and the alarm is triggered indicating that a high level has been attained within the vessel. Figure 1.3 Example of a high level alarm Both process alarm conditions are indicated by the red light emitting diode (LED) switching ON and staying ON (see diagram on page 3-7) and by the process alarm output. Failsafe alarm If any critical component fails during operation or if power to the unit is interrupted, the GM-16/GM-16R will fail in a safe manner - it notifies the user that something is wrong with the gauge and that the shown process condition (non-alarm or alarm) may not be accurate. In general, the failsafe alarm condition is indicated by the red LED. Triggered due to the failsafe alarm, however, the LED FLASHES rapidly, at a rate of 2 (two) flashes per second, instead of staying ON continually. It is also indicated by the failsafe alarm output (separate from the process alarm output). See Failsafe Alarm on page 3-4 for more details on the failsafe alarm conditions. Note: The red LED has third and fourth functions as well. Through calibration, the GM-16/GM-16R determines (or, if manually calibrated, is given) a time interval in which it measures the amount of radiation that reaches the tube and determines if there is an alarm condition. The red LED FLASHES once per time interval. Also, during calibration for the alarm condition, the red LED Stays ON. 1-6 GM-16 and GM-16R Technical Reference Manual
Introduction Nuclear materials notice This equipment contains radioactive source material that emits gamma radiation. Gamma radiation is a form of high-energy electromagnetic radiation. In many cases, only persons with a specific license from the U.S. NRC or other nuclear regulatory body may perform the following to the source holder: Dismantle Install Maintain Relocate Repair Test VEGA Field Service engineers have the specific license to install and commission nuclear gauges, and can instruct you to safely operate your level gauge. See page 1-10 for contact information. Note: Refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users Manual and the Radiation Safety Manual Addendum of Reference Information CD that came with the source holder and the appropriate current regulations for details. GM-16 and GM-16R Technical Reference Manual 1-7
Introduction Safety General There are no restrictions on using this instrument on the outside of closed metal vessels. Always follow the safety instructions in this manual and the country-specific installation standards (example: VDE regulations in Germany). Follow the safety regulations and accident prevention rules for your company and country. Manufacturer s responsibility Many of the requirements for safety are satisfied by the manufacturer, like VEGA, in the construction of containers and safety devices that limit the amount of radiation that reaches outside of the measuring area. That is, the source holder has been specially designed to minimize the amount of radiation to which a user can be exposed. More information is provided about the source and the source holder in Chapter 3: Operation. User s responsibility The remainder of the responsibility lies with the individuals who operate and service the equipment. A basic understanding of the nature of radiation and a respect for operating procedures is required. If the vessel on which the gauge is used can be entered by individuals, then it is important to follow proper lock-out procedures. For further information on lock-out'' and other user responsibilities, refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users manual and the Radiation Safety Manual References Addendum CD and the appropriate current regulations (NRC or Agreement State). Ohmart/vega also offers a series of Training Videos as well as regularly scheduled classes on the subject of Radiation Safety. To repeat, it is your responsibility to become familiar with and conform to your national and local regulations regarding the safe use of this equipment. 1-8 GM-16 and GM-16R Technical Reference Manual
Introduction Licensing requirements (U.S.A.) Also, be aware of the requirements in the United States to hold a license in order to operate a radioactive source. A license may be secured by one of two methods: Specific License - The GM-16/GM-16R Level Switch requires a Specific License. Only those who have applied for and received an NRC or Agreement State Specific License are considered to be Specifically Licensed. Those people should refer to their own license in order to determine what operations they are permitted to perform. General License - Certain model gauges are available under the NRC's General License provisions. (GM-16/GM-16R Level Switches are not available under a General License at this time.) The execution of the purchase of one of those models satisfies the requirements for obtaining a General License. A General License gives the holder permission only to mount the equipment in place. In order to turn it on, perform maintenance, or relocate it, however, on-site supervision must be secured from a specifically licensed person. Consult the metal label mounted on the equipment or contact VEGA for more details about General Licenses. When in doubt about radiation safety procedures, check the appropriate regulations which govern your equipment, or call the VEGA Corporation for assistance. GM-16 and GM-16R Technical Reference Manual 1-9
Introduction Customer service U.S. and Canada On-site field service is available in many locations. Often, a field service engineer is at your plant for startup. Field service engineers also provide assistance by phone during office hours. For emergencies (example: line shut down because of VEGA equipment), you can reach us 24 hours a day. Table 1.1 Contact information Tel (Monday Friday 8:00 A.M. 5:00 P.M. EST) +1 513-272-0131 Tel (emergencies: follow the voice mail instructions) +1 513-272-0131 Fax +1 513-272-0133 Field service e-mail fieldservice@vega.com Worldwide Contact your local VEGA representative for parts, service, and repairs. Have this information ready VEGA Customer Order (C.O.) Number Located on the source holder s engraved label Gauge s serial number Located on the exterior housing 1-10 GM-16 and GM-16R Technical Reference Manual
C HAPTER 2 Chapter 2INSTALLATION This chapter explains the procedures for unpacking, storing (if necessary), locating and mounting the equipment, as well as wiring instructions. Installation drawings are included at the end of the chapter to further aid in the installation of your GM-16/GM-16R. Shipping and transportation Shipment and transportation of devices containing radio-isotopes fall under extensive regulations. These regulations are internationally accepted and are published by the International Atomic Energy Agency. Shipments made by VEGA are in accordance with these regulations and are correctly identified on the container and the bills of lading. Should you need to return your GM-16/GM-16R for service, follow the instructions given on page 4-12. Also, for service or disposal, the following precautions should be observed: Contact VEGA regarding the proposed shipment. VEGA will provide any further or more specific instructions. Ensure that the source holder is securely locked in the OFF position. Pack the gauge in a sturdy (preferably wood) container. If it is open or damaged, additional lead shielding may be required. (VEGA can provide specific instructions for this.) Shipments may be made by a common carrier of your choice, but not by postal services. Bills of lading must note that the shipment contains radioactive material. Ensure that the shipping container is properly identified with the appropriate label. Notify VEGA as soon as the shipment is made, advising of the carrier, waybill number, and date of shipment. Note: NEVER make a shipment without first complying with the above, abridged requirements. GM-16 and GM-16R Technical Reference Manual 2-1
Installation Unpacking the equipment Caution: Before unpacking the equipment, refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users manual and the Radiation Safety Manual Referenes Addendum CD and the appropriate current regulations (NRC or Agreement State) for details. for instructions on handling equipment containing a radioactive source. Unpack the unit in a clean, dry area. Inspect the shipment for completeness, by checking against the packing slip, and for damage during shipment or storage. If the detector is included as a separate package in the shipment, inspect the assembly for damage that may have occurred during shipment or storage. If the unit was damaged during shipment, file a claim against the carrier, reporting the damage in detail. Any claim on The VEGA Americas, Inc. for shortages, errors in shipment, etc., must be made within 30 days of receipt of the shipment. Note: When equipment is unpacked, inspect each source holder included in the shipment to assure that the operating handle is in the OFF position. Should a source holder be found to have its operating handle in the ON position, place the handle in the OFF position and secure it. Most source holder models accept a lock. If the source holder model does accept a lock and there is no lock on it or it is not secured, call VEGA Field Service immediately for further instructions. 8:15-5:00 E.S.T., weekdays (513) 272-0131 After hours (513) 272-0135 2-2 GM-16 and GM-16R Technical Reference Manual
Installation Storing the equipment If it is necessary to store this equipment, do so in a clean, dry area which meets the Radiation Safety security criteria (a Restricted Area, as defined in the regulations). Avoid storage temperatures below freezing. For protection against mildew, mold and humidity, use appropriately sealed polyethylene bags with desiccant enclosed. Avoiding exposure to unnecessary dirt or moisture will prolong the life of the components. GM-16 and GM-16R Technical Reference Manual 2-3
Installation Installation procedures If your gauge, like most GM-16/GM-16R Level Switches, was shipped under a Specific License, verify that you are permitted to do the following before the arrival of VEGA's Field Service Engineer. If your license permits you to do so, proceed with the steps outlined below. If your gauge was shipped under a General License (a license not usually given for the GM-16/GM-16R), the following items should be completed before the arrival of the Field Service Engineer. 1. Allowing space for future maintenance, mount the gauge (source holder and detector/ electronics) per the instructions given in Mounting the equipment on page 2-5. Do not remove the source holder lock! 2. Make all wiring connections per the instructions in Mounting the GM-16 on adjacent vessels on page 2-7. 3. Have process available for calibration. Allow enough time with process for possible recalibration. The Field Service Engineer will need for you to be able to: Empty the vessel to provide the zero reference point. Fill the vessel in stages The above will enable the Field Service Engineer to: Do a two point calibration Establish a linearizer curve Further details on calibration can be found in Chapter 3: Operation. 2-4 GM-16 and GM-16R Technical Reference Manual
Installation Mounting the equipment Location on vessel An outline dimension view of the, GM-16/GM-16R Level Switch Housing, found in the Installation Drawings section, indicates the location of the GM tube detector within the Housing. Mount the GM-16/GM-16R with a bracket at the point on the vessel where the level is to be monitored. The red stripe on the housing indicates the GM tube (the radiation sensor) and should therefore be placed at the level for which an alarm is desired. The Housing can be placed either vertically or horizontally, in reference to the vessel, depending on space constraints and the amount of accuracy desired. When the axis of the GM tube is placed parallel to the surface of the process material, with its side facing the source, relay contact change over will be obtained when the set limit is exceeded by about one-half inch. When such a fine level limit is not required, a broad band of about 5 inches can be obtained by placing the detector axis perpendicular to the surface of the process material. This latter method is recommended for most applications and is normally used, although, for greater accuracy the horizontal position is preferred. In either case, an alarm is produced after the tube is obscured from (or exposed to) the radiation from the source. Although the level switch will tolerate a reasonable amount of vibration and still operate satisfactorily, it should not be mounted directly on bins or vessels that have vibrators attached. For these situations, the Level Switch should be mounted on adjacent building framework or special supports that have a minimum amount of vibration. Shock mounts are also available as an option. (See the Shock Mount diagram in the Installation Drawings ). Proper location of the instrument can sometimes mean the difference between satisfactory and unsatisactory operation. In planning for the location of the GM-16/GM-16R it is important to realize that any material between the source on one side of the process to be measured and the detector on the opposite side will affect the measurement. Internal obstructions, such as baffles, agitators, heater/cooler tubes, manways or ladders should be avoided if possible. Avoid locations where process build-up on the vessel walls may occur. That condition would have a gradual effect on the calibration of the gauge. GM-16 and GM-16R Technical Reference Manual 2-5
Installation Multiple installations of point level gauges in the same area (within 5 to 10 feet of each other) should be carefully planned. The gauges must be oriented so that the radiation of each source is detected by the appropriate sensor. Note: Try to locate the source holder in such a place that it will not become coated with process material, to ensure the continuing proper operation of the source ON/OFF mechanism. Many regulatory agencies (Le., the U.S. NRC) require periodic testing of the ON/OFF mechanism. Refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users manual and the Radiation Safety Manual Referenes Addendum CD and the appropriate current regulations (NRC or Agreement State) for details. Whether or not the source and detector can both be mounted outside the vessel, on opposite walls or on a chord depends on vessel diameter and wall thicknesses. When vessels exceed approximately 30 feet, the source size becomes very large. Or, if there is a thick firebrick or similar wall absorption, use of a well for the source is desireable so that the radiation need go through only one wall. Window holes in heavy wall insulation, with dead space or lighter weight insulation in the hole, help greatly to reduce source size, but alignment of the bore of the two holes is critical. Figure 2.1 Mounting the GM-16 on an isolated vessel Consideration of the area usage under empty vessel or low level conditions must be made, to be sure that operating or repair personnel will not receive excessive radiation. Access inside vessel On most common installations, sources are sized so that under normal operating conditions outside the vessel there will be under 5 MR/hr at 12 inches from the source holder or on the opposite side of the vessel from the source. If a maintenance person goes down into the empty vessel with the source open, they would receive a much higher dosage rate. Interlocking the source shutter on-off handle with a padlock and locking the vessel access door is a good practice when such possibilities exist. 2-6 GM-16 and GM-16R Technical Reference Manual
Installation Orientation with other vessels When multiple adjacent vessels are quipped with nuclear level gauges, orientation of the source beams must be considered in light of the over-all vessel arrangement. With two adjacent tanks the sources should each be on the inside looking out. Otherwise, the two detectors will see a component of radiation change from level changes on the opposite vessel. If more than two vessels are present, the radiation beams must be aligned to avoid striking a detector on another vessel. Figure 2.2 Mounting the GM-16 on adjacent vessels GM-16 and GM-16R Technical Reference Manual 2-7
Installation Wiring the equipment The contacts of the GM-16/GM-16R relays are rated for 2 amperes at voltages up to 250 Vac or 220 Vdc. The 2 ampere rating, for both ac and dc, is for resistive loads where the maximum switched power is 60 watts or 125 volt-amperes. The CSA ratings for the 2 ampere relay are:.6 A at 125 Vac (resistive);.6 A at 110 Vdc (resistive); or 2 A at 30 Vdc (resistive). If a larger dc or ac load is to be used, the alarm contacts should be used to operate another control device, such as a motor contactor or power relay, which is capable of switching the necessary load. (A 10 ampere relay is also available. Its rating (standard and CSA) is 10 amps ac at 240 V and 8 amps dc at 24 V, and is for loads where the maximum switched power is 200 watts, dc or 2000 volt-amperes, ac. The CSA ratings are: 113 HP at 120 Vac or 112 HP at 240 Vac.) The relay is de-rated for inductive loads. The certified Electrical Connections Drawings for the GM-16 or the GM-16R Level Switch (depending on which gauge type you have purchased) are included with the Installation drawings on page 2-11. Follow the drawing notes and the steps that follow for switching jumpers and for making the input and output connections. Caution: checked! DO NOT APPLY POWER until wiring is thoroughly The following procedure should be followed for reliable equipment operation: If you have purchased the GM-16 level switch, bypass steps 1 through 8 below, which are for users of the GM-16R, and begin with step 9. Interconnect For connecting the GM-16R Detector Housing to the GM-16R Electronics Housing. Detector Housing 1. Open the end of the Detector Housing by unscrewing the pipe cap. Loosen the screw holding the chassis in the pipe housing. Twist and pull the chassis out enough to gain access to the terminal block at the far end of the chassis. 2. Using cable supplied by the user (cable should meet the requirements listed in Chapter 4: Product specifications ) make the four connections as shown on the Electrical Connections for the Detector Housing drawing. (Connections are made by loosening the screw on the top of the terminal block, inserting the wire - stripped about 1/4" - into the front of the block, and tightening the screw. 2-8 GM-16 and GM-16R Technical Reference Manual
Installation 3. The cable should run through conduit to the Electronics Housing. Conduit runs should be continuous and protection should be provided to prevent conduit condensed moisture from dripping into any of the housings or junction boxes. This may be done by using sealants in the conduit, or by arranging the runs so that they are below the entries to the housings and using weep holes where permitted. 4. A conduit seal-off must be used in the proximity of the housing (actual distance as required by local code) when the location is in a hazardous area. 5. Fasten the 3/4" conduits and pull the wiring through the conduits to the Electronics Housing. When only one conduit hub is used, the other must be plugged to prevent the entrance of dirt and moisture. 6. Replace the chassis into the housing. Replace the screw holding the chassis in place. Replace the end cap. Electronics Housing 7. Open the end of the Electronics Housing by unscrewing the pipe cap. Loosen the screw holding the electronics chassis in the pipe housing. Remove the pluggable terminal block, leaving the ground to the housing connected. Twist the electronics chassis and pull the chassis out enough to gain access to the terminal block at the far end of the board. 8. Pull the cable from the Detector Housing into the Electronics Housing through the conduit hub. Make the electrical connections as shown on the Electrical Connections for the Electronics Housing drawing (and as described in Step 2 above). Proceed to step 10. Jumpers 9. Open the end of the housing by unscrewing the pipe cap. Loosen the screw holding the electronics chassis in the pipe housing. Remove the pluggable terminal block, leaving the ground to the housing connected. Twist and remove the electronics chassis and pull the chassis out enough to gain access to the circuit board. 10. Check the jumper (JP1) on the circuit board to verify that it is set for the correct power input, either 110 volts or 220 volts. (JP1 is located on the rear, left side of the chassis.) Refer to the Electrical Connections Drawing in the Installation drawings. 11. Set the jumper (JP5) on the Failsafe Relay to the normally open or normally closed position. (JP5 is located behind the pluggable terminal block, and in front of the relays.) Keep in mind that normally open refers to the relay contact in the nonenergized state (which is the alarm state). Hence, when the GM-16/GM-16R is operating (in the non-alarm state) the normally open contact will be closed and the normally closed contact will be open. 12. Place the electronics chassis back in the pipe housing and tighten the screw. GM-16 and GM-16R Technical Reference Manual 2-9
Installation Input and Output The ac power source must be maintained between 105 and 125 volts or 207 and 253 volts. The GM-16/GM-16R should be connected to a voltage supply that can not be turned off inadvertently. This should be a clean, transient-free supply such as a lighting panel. Do not use a line that is connected to a large motor, welding equipment, solenoids, etc., as doing this may adversely affect the performance of the gauge. Power should be applied to the measuring assembly continuously. The use of cables not furnished by VEGA should be as specified on the drawings. All cables should be inspected for damage or imperfections before use. Exercise extra care in the pulling, routing, and termination of interconnecting wiring to help eliminate troubleshooting and equipment downtime through the operating life of the system. Conduit runs for input and output should be as described in steps 3 and 4 above. 13. Fasten the 3/4" conduits and pull the power supply and alarm output wires through the conduits and housing. If only one conduit hub is used, the other conduit hub must be plugged to prevent the entry of dirt and moisture. All wiring is done through the pluggable terminal block. Wires need to be stripped about 1/4", placed into the square opening (underneath), and tightened into place by the screw (front). 14. Connect the alarm lines at pins 1 through 8. Pins 7 and 8 are for the Failsafe Alarm. Pins 1 through 6 are for the Process Alarm outputs. (See Electrical Connections Drawing in Installation drawings ) Note: For information on connecting the GM-16/GM-16R to a personal computer (RS-232 or RS485), contact the VEGA Americas, Inc. 15. Connect the three power supply wires at pins 9, 10, and 11. (See Electrical Connections Drawing in Installation drawings ) 16. Replace the pluggable terminal block. Caution: Do NOT begin operation of the gauge (open the source holder shutter) unless you are specifically licensed to do so.refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users manual and the Radiation Safety Manual Referenes Addendum CD and the appropriate current regulations (NRC or Agreement State) for details. 17. Replace the pipe cap until you are ready to calibrate and begin operation. 2-10 GM-16 and GM-16R Technical Reference Manual
Installation Installation drawings VEGA recommends following the certified drawings that they provide for your application. The drawings that follow may be useful for reference. GM-16 and GM-16R Technical Reference Manual 2-11
Installation Figure 2.3 D-51683 Outline of the detector s shock mount assembly 2-12 GM-16 and GM-16R Technical Reference Manual
Installation Figure 2.4 D-52057 GM-16 electrical connections GM-16 and GM-16R Technical Reference Manual 2-13
Installation Figure 2.5 D-52301GM-16R electrical connections 2-14 GM-16 and GM-16R Technical Reference Manual
Installation Figure 2.6 D-52014 GM-16 detector housing with 2 hubs GM-16 and GM-16R Technical Reference Manual 2-15
Installation Figure 2.7 D-51855 GM-16 Detector housing with 2 hubs - CENELEC approval 2-16 GM-16 and GM-16R Technical Reference Manual
Installation Figure 2.8 D-52311 Outline of GM-16R detector and electronics housing GM-16 and GM-16R Technical Reference Manual 2-17
Installation Figure 2.9 D-52312 Outline of GM-16R detector and eletronics housings - CENELEC approval 2-18 GM-16 and GM-16R Technical Reference Manual
C HAPTER 3 Chapter 3OPERATION This chapter discusses the various components of the GM-16/GM-16R and their functions. The signal processing, which occurs during normal operation, is explained. Also discussed is preparation for calibration of the gauge, which takes place through the computerized electronics. Components of the gauge Radioactive source The standardized types of radioactive sources used in a density measurement system are Cesium-137 and Cobalt-60. Cesium-137 has a half-life of 30 years and a low energy gamma radiation (0.66 MeV) which is readily absorbed. Consequently, Cesium-137 is used where maximum instrument sensitivity is required. Cobalt-60 has a half-life of 5.3 years and much higher energy radiation (1.2 and 1.3 MeV); it is used for applications requiring greater penetration power. The activity (measured in millicuries or becquerels) of the source is selected to fit the application. All sources commonly used are double sealed in welded stainless steel capsules. The diameter of the cylindrical-shaped source capsule is typically 1/2". The capsule is 3/4" or 1-1/2" long for point sources, depending upon the activity. Note: For more information on the radioactive source and the handling of radioactive materials refer to the Radiation Safety for U.S. General and Specific Licensees, Canadian and International Users manual and the Radiation Safety Manual Referenes Addendum CD and the appropriate current regulations (NRC or Agreement State) for details. GM-16 and GM-16R Technical Reference Manual 3-1
Operation Source holder VEGA source holders are designed to provide radiation safety by reducing the radiation intensity to a safe level for handling and servicing. Most source holder designs also provide a collimator, which directs the radiation beam directly through the process and toward the detector. The holders are either steel weldments filled with lead or, in the case of fireproof models, solid cast-iron. Most source holder designs have provisions for shuttering, or moving the source to an OFF position, which completely encloses the source thereby providing an additional measure of safety for handling and servicing purposes. Some applications require the source to be mounted in a source-well within the vessel. In these cases, a lead and steel shipping and storage container is included to provide safe storage at any time the source must be removed from the source-well. A source container which bolts directly to the source-well flange may be provided to allow the source to be pulled directly into a shielding container during vessel maintenance. A yellow and magenta warning tag, showing the type and quantity of radioactive material, is affixed to the source holder. Caution: Abandonment or disposal of a source is prohibited unless transferred to persons specifically licensed by the NRC or an Agreement State. Malfunction of the source holder should be reported to The VEGA Americas, Inc. for repair or replacement. Geiger Mueller (GM) detector The radiation sensor is an VEGA Geiger Mueller (GM) detector. This is a hollow metal tube filled with an inert pressurized gas (usually halogen). As radiation strikes the tube, there is a partial ionization of the inert gas. The metal tube contains two electrodes: the anode, which is a positive electrode and the cathode, which is a negative electrode. A large bias voltage (700 Vdc), which is provided by a Zener diode regulated power supply, is applied to the cathode to enhance the attraction of ions. anode (+ ) gas detector output Figure 3.1 How the GM tube works cathode ( ) 3-2 GM-16 and GM-16R Technical Reference Manual
Operation When gas is ionized, positive ions are attracted to the negative electrode, while negative ions are attracted to the positive electrode. Thus, an electric current is generated. The output of the GM tube is a series of pulses. The number of pulses per second is directly proportional to the radiation field intensity at the tube. The pulses are ac coupled through capacitor C3 (see Schematic in Chapter 4: Reference Drawings ) to Darlington transistor Q1. Transistor Q1 buffers the pulses and provides a low impedance signal to the microprocessor. In the GM-16/GM-16R, one, two, or six Geiger Mueller tubes may be used depending upon the amount of sensitivity required and the response time needed. The graph on the following page illustrates sample curves for one, two, and six tubes. Although not exact, this graph gives an indication of what response times can be achieved and field strengths detected with different numbers of tubes. (See also Table 3.2: "Field Intensity At The Detector") The field intensity along the x-axis indicates the absolute change in field intensity. Figure 3.2 Field intensity versus response time GM-16 and GM-16R Technical Reference Manual 3-3
Operation Failsafe Alarm The GM-16/GM-16R Level Switch is designed to fail in a safe manner if any critical component fails during operation. The failsafe alarm is triggered in four different situations: 1. If there is a failure in the GM-16/GM-16R circuitry or in the detector. 2. If the EEPROM does not retain the calibration data (i.e. during a power loss). A distinction can be made between these two failsafe conditions by removing power to the unit and then restoring it. If the red LED begins flashing immediately then the calibration data in the EEPROM is corrupted. If there is a 30 second delay before the LED begins flashing then the problem is with the GM-16 tube or circuitry. 3. If, when auto-calibrated, the GM-16/GM-16R determines that a time interval greater than 2 minutes (10 minutes if you have software version 2.00L) is needed to accurately determine the process condition. This determination will be made immediately after the calibration is complete. 4. If power to the unit is interrupted. The LED will operate but the failsafe alarm output will be triggered. Each of these conditions causes the failsafe circuit Relay 2 to de-energize, resulting in an alarm condition. The failsafe alarm is indicated by the FLASHING red LED (except while the power is off) and the failsafe alarm output. Background radiation is sufficient for the tube to generate enough counts to keep the failsafe circuit in the non-alarm condition during normal operation. Watch Dog Timer The GM-16/GM-16R Level Switch is also equipped with a Watch Dog Timer, or power line supervisor. The watch dog must be toggled by the central processing unit (CPU) every 50 milliseconds. If the watch dog is not toggled, in the event of a power failure, power spike or CPU lock-up, it will initiate a reset cycle. An EEPROM (electronically erasable programmable read-only memory) retains the last calibration and, when power is restored, will return the GM-16/GM-16R to the mode (Stand-by or Operate) which it was in prior to the failure. 3-4 GM-16 and GM-16R Technical Reference Manual
Operation Calibration of gauge After making the initial decision of whether the GM-16/GM-16R Level Switch is to be used as a low level or a high level detector, mounting, installation, and proper testing, it is time for calibration. The GM-16/GM-16R can be either autocalibrated or calibrated manually. When auto-calibrated, the GM-16/GM-16R, using an algorithmic calculation, determines the time interval that results in the best data (i.e. quickest response time without false alarm triggering.) Choosing auto-calibration or manual calibration Auto-calibration In most cases, auto-calibration achieves the best possible time interval. For this reason, we recommend doing auto-calibration first. If the time interval set through auto-calibration is not acceptable, then manual calibration may be done to change the time interval. Manual calibration If a response time faster or slower than that automatically calibrated is desired, the switch must be manually calibrated. A longer time interval - slower response time - may be necessary if excessive false triggering occurs. Keep in mind that reducing the time interval (achieving a faster response time) can iead to false triggering. Care should be taken, when manually calibrating, to assure that the time interval is one in which consistent results (allowing for statistical error) can be obtained. If manual calibration is chosen, determination of acceptable time intervals can be achieved in one of two ways: Use the calculations below as a guideline. (These are the calculations that the GM-16/ GM-16R uses when autocalibrating.) Determine the time interval established through autocalibration by observing the time between flashes of the red LED - this flashes once per time interval. This time can then be used as a reference for the time interval appropriate for your situation. After determining the desired time interval, proceed with the Calibration procedure. Use the manual calibration instructions (step 3.b.). If auto-calibration is chosen, then skip these calculations and go directly to the Calibration section which follows. GM-16 and GM-16R Technical Reference Manual 3-5