Thermal Considerations

It is very important to appropriately dissipate the heat generated during TestScale system operation. You must plan for the thermal conditions of your application throughout design, development, and validation.

Understanding TestScale Thermal Specifications

Your TestScale system may use any number of enclosure sizes, thermal solutions, materials, and room conditions, therefore TestScale thermal specifications are determined independently of such external variables.

  • In-fixture backplanes—TestScale thermal performance is determined by the cooling effectiveness of the enclosure design and can be validated by reading the internal operating temperature from the onboard temperature sensors.
  • Rackmount backplanes—TestScale thermal performance is determined by the specified external ambient temperature and cooling from the provided fan. You can also read the internal ambient temperature from the onboard temperature sensors.
External ambient temperature 0 °C to 55 °C Ambient temperature refers to the temperature of the room, environment, or enclosure in which TestScale is installed. For rackmount backplanes, external ambient temperature is the temperature measured directly at the enclosure fan inlet or air intake.
Recommended maximum internal operating ambient temperature <70 °C The onboard temperature sensors on the backplane return the internal ambient temperature reading as a reference for user validation. Specifications for all TestScale I/O modules and modular instruments account for the recommended internal ambient temperature rise.
Over-temperature protection for temperature-sensitive modules An over-temperature condition occurs when the onboard temperature reading of temperature-sensitive modules (not the backplanes) exceeds the threshold limit stated in the module specifications. When an over-temperature condition occurs, the module will be automatically disabled.

Designing the TS-15000 Enclosure to Optimize Cooling

You must design the TS-15000 enclosure to keep the assembly within the supported ambient temperature range. While a smaller enclosure may offer a compact form factor, it must provide enough space for both the electrical components and adequate cooling. If using fans in the enclosure design, you can reduce the amount of space being utilized if fan placement allows for optimal airflow. If you are not using fans in the enclosure, you must maintain adequate clearance between the backplanes and surrounding equipment or blockages to ensure proper cooling for the backplanes and modules installed into the TS-15000 enclosure.

If using fans in the enclosure, place them where the airflow is not impeded, allowing air to flow parallel to the TestScale I/O modules and backplane PCBs.

Refer to the Internal Operating Temperature Sensor Reading Use Cases topic for fan placement examples.

Calculating TestScale Thermal Dissipation

All TestScale backplanes and modules experience power loss as thermal dissipation. Refer to your backplane and module specifications for the thermal dissipation specification. To estimate the maximum thermal dissipation, add together all the thermal dissipation specification values from the backplanes and modules in your TestScale configuration.

Validating the TestScale Temperature

The TestScale backplane includes eight onboard temperature sensors to validate thermal solution by monitoring thermal performance during validation and deployment. The sensors validate onboard temperatures that can be used to determine the approximate internal operating temperature. This approach is called digital validation.

For digital validation, ensure that the maximum internal operating temperature reading does not exceed the maximum internal operating temperature listed in this document.

Complete the following steps to read the onboard sensor temperature using a LabVIEW VI.

  1. Launch LabVIEW.
  2. Start the session with Initialize Session and set the target to localhost.
  3. Call the Create Filter to create a filter to search the device.
  4. Use the Property Node to configure the filter with the below parameters:
    Expert Info:Expert Name daqmx
    Devices & Chassis:Connects To Bus Type USB
    Expert Info:User Alias <TestScale Device Name>
  5. Call the Find Hardware and Index Array to identify the device.
  6. Use the Property Node to read the onboard temperature information.
    Alias <TestScale Device Name>
    TempCount <Number of Temperature Sensors Available>
    TempNames <Temperature Sensor Name>
    TempReadings <Temperature Readings>
  7. Click Close to end the session.

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Internal Operating Temperature Sensor Reading Use Cases

This section examines several uses cases to demonstrate how the configuration of enclosed electronics and cooling affect the internal operating temperature sensor reading. The use cases shared the following configurations and procedures.

Test Procedure

Testing was conducted at room temperature.

  1. TestScale was configured and the DUT was mounted as described here and in the use case.
  2. The system stressing VI was configured and run.
  3. The system was allowed to reach a steady state.
  4. Temperature sensor readings were logged.
  5. Logged sensor readings were extrapolated to an external ambient temperature of 55 °C.

TestScale Software Configuration

During testing, a system stress and verification VI is run with the applicable configuration.

To configure TestScale for low-power dissipation applications:

  1. Configure all Core Module I/O to output mode and toggle these DIOs at maximum frequency. In the worst case, draw the maximum current from these DIOs with resistive loads, with one of the channels connected to 30 V to simulate a fault condition.
  2. Configure the programmable power supply module to output a constant 5 V and draw 20 mA with a resistive load.
  3. Configure all I/O modules to draw maximum power by toggling or sampling at the maximum data rate while using a resistive load to draw maximum current from output channels and simulate fault conditions.

To configure TestScale for high-power dissipation applications:

  1. Configure all Core Module I/O to output mode and toggle these DIOs at maximum frequency. In the worst case, draw the maximum current from these DIOs with resistive loads, with one of the channels connected to 30 V to simulate a fault condition.
  2. Configure the programmable power supply module to output a constant 6 V and draw 3 A with a resistive load.
  3. Configure the load card power through the front I/O connector using jumper wires.

TestScale Hardware Configuration

To configure the TestScale hardware for low-power dissipation applications, the following six modules were used:

  • 1 x Core module configured at 1.7 W
  • 1 x programmable power supply module configured at 1.3 W (placed in slot 3)
  • 4 x I/O modules configured at 1.5 W each

To configure the TestScale hardware for high-power dissipation applications, the following six modules were used:

  • 1 x Core module configured at 1.7 W
  • 1 x programmable power supply module configured at 10.0 W (placed in slots 2 and 3)
  • 2 x load cards configured at 1.5 W each
  • 1 x load cards configured at 2.5 W (placed in slot 1)

Enclosure Specifications

Feature Measurement
Aluminum enclosure 2 mm thick, 140 mm (H) × 500 mm (W) × 350 mm (D)
Vent area (side) 8,322 mm2
Vent area (opposite fan) 5,475 mm2
Vent area (top) 4,800 mm2

Fan Specifications

Feature Measurement
Manufacturer (part number) Nidec (D1225C12BBZP-50)
Dimensions 120 mm × 120 mm × 25 mm
Rated speed 5,400 rpm
Maximum airflow 4.25 m3/min (150 cfm)
Rated voltage 12 VDC

Use Case: High-Power Configuration with Side-Mount DUT and Side Vent

This example uses TestScale in a high-power configuration. The enclosure vent is on the side of the enclosure at a right angle to the enclosure fan. The DUT is side-mounted inside the enclosure directly in front of the fan at a distance of 45 mm.

The DUT is oriented to optimize airflow through the unit, as illustrated in the following diagram.

Figure 20. Airflow with Fan and Vent at Right Angles with Side-Mount DUT

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Test Results

Temperature sensor results for this configuration show smaller (worse) operating margins for areas that are further away from the fan. These results also reflect smaller (worse) operating temperature margins than when the vent is positioned opposite the fan. The test was conducted at room temperature and the results were extrapolated to an ambient external temperature of 55 °C. Test results can be found in the following table.

Table 7. Extrapolated Internal Operating Temperature Sensor Readings
Name Sensor Measurement, °C Margin, °C (Relative to 70 °C)
TempSensor1 U41 59.2 +10.8
TempSensor2 Q14 58.6 +11.4
TempSensor3 U42 57.1 +12.9
TempSensor4 Q15 56.2 +13.8
TempSensor5 U43 56.5 +13.5
TempSensor6 Q16 55.5 +14.5
TempSensor7 U44 55.6 +14.4
TempSensor8 Q17 54.6 +15.4

Use Case: High-Power Configuration with Side-Mount DUT and Vent Opposite Fan

This example uses TestScale in a high-power configuration. The enclosure vent is opposite the enclosure fan. The DUT is side-mounted inside the enclosure directly in front of the fan at a distance of 45 mm.

The DUT is oriented to optimize airflow through the unit, as illustrated in the following diagram.

Figure 21. Airflow with Fan and Vent in Alignment with Side-Mount DUT

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Test Results

Temperature sensor results for this configuration show smaller (worse) operating margins for areas that are further away from the fan. The test was conducted at room temperature and the results were extrapolated to an ambient external temperature of 55 °C. Test results can be found in the following table.

Table 8. Extrapolated Internal Operating Temperature Sensor Readings
Name Sensor Measurement, °C Margin, °C (Relative to 70 °C)
TempSensor1 U41 58.1 +11.9
TempSensor2 Q14 57.6 +12.4
TempSensor3 U42 56.7 +13.3
TempSensor4 Q15 55.9 +14.1
TempSensor5 U43 56.3 +13.7
TempSensor6 Q16 55.3 +14.7
TempSensor7 U44 55.4 +14.6
TempSensor8 Q17 54.5 +15.5

Use Case: High-Power Configuration with Bottom-Mount DUT

This example uses TestScale in a high-power configuration. The enclosure vent is opposite the enclosure fan. The DUT is bottom-mounted inside the enclosure directly in front of the fan at a distance of 125 mm.

The DUT is oriented to optimize airflow through the unit, as illustrated in the following diagram.

Figure 22. Airflow with Fan and Vent in Alignment with Bottom-Mount DUT

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Test Results

Temperature sensor results for this configuration show better operating margins for areas that are further away from the fan. In this configuration, the DUT orientation allows hot air to effectively rise away from the DUT.

Test conditions for this configuration differed from test conditions for other high-power configurations. The differences are as follows:

  • The volume of the enclosure used for this test case was smaller by roughly 40%.
  • The vent opening area was smaller by roughly 32%.
Table 9. Extrapolated Internal Operating Temperature Sensor Readings
Name Sensor Measurement, °C Margin, °C (Relative to 70 °C)
TempSensor1 U41 57.2 +12.8
TempSensor2 Q14 56.5 +13.5
TempSensor3 U42 56.8 +13.2
TempSensor4 Q15 55.9 +14.1
TempSensor5 U43 56.5 +13.5
TempSensor6 Q16 55.4 +14.6
TempSensor7 U44 55.7 +14.3
TempSensor8 Q17 54.8 +15.2

Use Case: Low-Power Configuration with no Enclosure Fan

This example uses TestScale in a low-power configuration. The enclosure has no fan. The DUT is side-mounted inside the enclosure beneath a vent on top of the enclosure.

Figure 23. Airflow with No Fan and Vent Above Side-Mount DUT

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Test Results

For use-cases where there is no fan, apply the following suggestions to keep the internal operating temperature below <70 °C.

  • Operate TestScale in a low-power configuration.
  • Operate at a lower ambient temperature.
  • Increase the size of the enclosure vent.

When test results at room temperature are extrapolated to an ambient external temperature of 55 °C, this configuration exceeds the recommended maximum internal operating temperature sensor reading of <70 °C. Test results extrapolated to an ambient temperature of 50 °C approach, but remain below <70 °C.

Table 10. Extrapolated Internal Operating Temperature Sensor Readings
Name Sensor Measurement, °C Margin, °C (Relative to 70 °C)
TempSensor1 U41 67.6 +2.4
TempSensor2 Q14 67.0 +3.0
TempSensor3 U42 72.4 -2.4
TempSensor4 Q15 71.9 -1.9
TempSensor5 U43 73.4 -3.4
TempSensor6 Q16 72.5 -2.5
TempSensor7 U44 71.4 -1.4
TempSensor8 Q17 70.4 -0.4