Environmental Chamber Webinar Series Benefits of "Part Temperature Control" May 2017
Why do we care about part temperature? How does a DUT perform when exposed to hot and cold temperatures? Performance at temperature extremes. Stresses from expansion and contraction. What is the characteristic of a DUT at a particular temperature? Examples: Temperature coefficient of oscillators, voltage regulators, capacitors, resistors. Parameters change with every degree change in temperature (Hz/ C, mv/ C, Ω/ C). 2
Airflow in the chamber Temperature Sensor Fan Heater Evaporator (Cooling Coil) Airflow Air Flow Air Plenum with cover removed 3
Airflow in the chamber Air Plenum Air Plenum Airflow Airflow Airflow pattern in Models 107, 123, 1000 Series, and 3000 Series Airflow pattern in Model 115A 4
Standard temperature controller display Temperature controllers in chambers display the air temperature. Air temperature sensor is placed in the air discharge area (or occasionally the air return area). achieves the smallest short-term variations in temperature (Control Tolerance spec typ. ±0.5 C). Correlates to DUT temperature but is NOT the DUT temperature. Air Plenum with cover removed 5
What about thermal mapping? Thermal mapping measures the temperature uniformity in the workspace (Uniformity specification typ. ±1.0 C). Typically 9 points of measurement. Performed in an empty chamber unfortunately, this is not how the chamber will really be used! False sense of security. Useless when you really want to know the DUT temperature. 6
Why is DUT temperature is different? Wall temperature needs time to stabilize. Window needs time to stabilize (where applicable). Insulation losses. Mass of product needs time to stabilize. 7
How long does it take for my DUT to stabilize?????????? You would need to have an independent temperature sensor on your DUT and characterize it. 8
What happens with air control only? All temperature controllers have "Proportional Band" (PB) PB is like putting your foot on the brake BEFORE you reach the stop sign to prevent overshooting the sign. PB is typically 5 C. This means that the heating or cooling action will begin to throttle (slow down) 5 C before your temperature setting (set point). Approach to final value is somewhat asymptotic. PB adds to the DUT temperature lag. Chamber performance spec does not include effect of PB when approaching the Set Point. 9
Example of Proportional Band 10
Example of Air Temperature Control Part Temperate lags the Air Temperature Part Temperature settles 1.5 C lower than the Air Temperature Set Point of +85 C Longer time to settle = longer test time Test results may not be valid because DUT never reaches the exact temperature set point 11
With air control only, need to add time You would need to characterize the process by measuring your DUT temperature independently. Minutes/hours longer than when the chamber's temperature controller indicates you have reached Set Point. DUT may not ever reach the desired temperature (Offset). Iterative process, will be different depending on the DUT and loading in the chamber. Consequence of not characterizing = false data. 12
Air Control = Invalid test if no considerations are made DUT never quite reaches the temperature setting. Longer test time if you actually wait for the DUT to reach Set Point. 1 lb static load 13
There is an alternative Cascade Control Cascade Control is the technical name for a two-loop control system where the air temperature (Inner Loop) is determined by deviation of the part temperature (Outer Loop) from its Set Point. With Cascade Control, the air temperature is biased higher/lower in a precise manner for the fastest response at the DUT. Note: Cascade Control and Cascade Refrigeration are two completely unrelated terms. 14
"Deviation Cascade" TestEquity uses "Deviation Cascade" control mode Air Temperature is allowed to deviate by up to ±15 C. Examples: Set Point of 85 C, air temperature allowed to reach maximum deviation of 85+15 or 100 C in a precisely controlled manner. Set Point of -40 C, air temperature allowed to reach maximum deviation of -40+(-15) or -55 C in a precisely controlled manner. Air temperature is lowered as DUT approaches Set Point in a precisely controlled manner. DUT not in danger of going to maximum deviation temperature. 15
Air temperature biased in a precise manner 16
Cascade Control (Part Temperature Control) Max deviation set for +15 C Air temperature is biased higher/lower in a controlled manner for the fastest response at the DUT. 1 lb static load Max deviation set for 15 C 17
Air Control Comparison DUT never quite reaches the temperature setting. Longer test time if you actually wait for the DUT to reach Set Point. 1 lb static load 18
Pluses and Minuses Pluses Shorter test time More accurate results Minuses Sensor must be attached to DUT at all times If sensor is not attached air temperature will be unstable unless Cascade Control is disabled. You may not want to use if DUT is dissipating heat. 19
F4T Screen with Cascade Control Enabled "Temperature" is the DUT sensor "Temperature" and "Air Sensor" read differently DUT sensor must be attached to DUT 20
F4T Screen with Cascade Control Disabled Air Control key is pressed to disable Cascade Control "Temperature" is the same as "Air Sensor" 21
Simple Set Point Enable This function is similar to turning Air Control ON. If you leave Air Control OFF and turn Simple Set Point Enable ON, the F4T will attempt to control the temperature at the Air Sensor. However, the Guaranteed Soak and Wait For Process will be controlled by the Part Sensor. 22
Part Temperature Control option Standard on Model 155 Benchtop Chamber Option at time of chamber purchase for other models: F4T-T-CASCADE, +$375 Upgrade kit for older chambers: F4T-T-CASCADE-UG, $2,202 For temperature chambers only www.testequity.com/cascade for more information 23
Thank You! 24
Questions? 25