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Thunder Support Document

High Dew Point Calibration

Calibration at dew points above ambient temperatures...

General Eastern Model D-2 Dew Point Sensor.

Figure 6.1

A typical dew point sensor shown here is the General Eastern Model D-2.



Dew Point Sensor in Chamber.

Figure 6.2

Install the dew-point sensor in the test chamber as shown in Fig 6.2 in this example a shelf is used to position the dew-point sensor in-line with the access port.

The temperature probe from the test instrument DUT will be taped to the back wall of the test chamber with the 2500 chamber temperature sensor.

A tee fitting is installed at the chamber inlet for connection to the dew-point sensor; note an open tube on the opposite end of the tee fitting is used to direct the additional flow into the test chamber. The outlet of the dew-point sensor is connected to clean ¼” Teflon tubing, the sample line should be sloped downward from the dew-point sensor to prevent condensation in the tubing from draining back to the dew-point sensor.



Flow Meter Along with the Dew Point Measuring Device.

Figure 6.3

The outlet tubing is connected to an adjustable valve and flow meter. Change the 2500 flow rate to 10 SLPM, adjust the valve to a flow rate of 1 SLPM at the flow meter.



Dew Point Measuring Device with No Flow Meter.

Figure 6.4

Note the flow meter will be removed during the calibration due to the potential condensation at the outlet tube.



A Condensate Trap is Shown.

Figure 6.5

A condensate trap can be used to collect condensing moisture before the flow meter as shown in Fig 6.5.



HumiCalc Shown with a Dew Point Setting of 35.0 C and Test Temp at 40.0 C.

Figure 6.6

The target test point for this calibration is +35 °C dew-point, to accomplish this elevated dew-point it will be necessary to operate the test chamber at a test temperature of 40 °C.

Using HumiCalc© we can calculate the humidity set point at 40 °C test temperature to achieve the desired dew-point. Please view HumiCalc© example screen Fig 6.6.

Select Normal Mode, the known value will be Dew-Point DP, the test temperature needs to be higher than the known dew-point DP, enter 40 °C test temp, enter 35 °C for the known dew-point DP value. The %RH calculated is 76.20 %RH.


Begin the Calibration Test

You should begin the calibration test at a lower %RH set point until the test chamber temperature is within 2 degrees of the desired set point of 40 °C, as an example start the test at 20% RH until the test chamber actual displays 38 °C, change the humidity set point to 76.20% RH and allow the 2500 to stabilize for a minimum of 30 minutes. Wait for the DUT dew-point indication to stabilize before recording the calibration point.



Input the Actual Readings From the 2500 Screen.

Figure 6.7

Input actual humidity, chamber temperature and chamber pressure, press calculate, HumiCalc© will display the generated dew-point as shown in Fig. 6.7. A normal test time duration of 2 hours will be required to complete this test.



Input the Figures Found On the 2500 Screen.

Figure 6.8

Using HumiCalc© calculate the actual generated dew-point using the values displayed on the 2500 screen Figure 6.8.



Note the Condensation in the Tube.

Figure 6.9

DUT display at a humidity set point of 77.39 calculated dew point 34.999, test temperature of 39.71.



Under the Mode Menu Select Dew Point.

Figure 6.10

Using ControLog Automation software under Mode menu tool bar select Dew Point.



Enter 40.0 C for the Sat Temp Set Point.

Figure 6.11

In ControLog®, click on the the Saturation Temp Field under Control Parameters, the Saturation Temp dialog box will appear, change the test temperature to 40 °C.



Enter 35.0 C for the Dew Point Setpoint.

Figure 6.12

Next click on the the Dew Point Field under Control Parameters and enter 35.0 °C and Click OK.



Under the Run Menu Select Generate.

Figure 6.13

On the Run menu select Generate and begin the calibration test.



What a Normal Graph Should Look Like.

Figure 6.14

After the generation cycle, figure 6.14 shows what a normal run should look like.

You should begin the calibration test at a lower dew point until the test chamber temperature is within 2 degrees of the desired set point of 40 °C, as an example start the test at 20 °C dew point until the test chamber actual displays 38 °C, change the dew point set point to 35 °C dew point and allow an additional 30 minutes for stabilization.

A normal test time duration of 2 hours will be required to complete this test.


Click here to continue with the next calibration session.

Please contact support@thunderscientific.com should you have questions or problems using the procedure. We always appreciate your comments and feedback.

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