High Dew Point Calibration
Calibration at dew points above ambient temperatures...
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Figure 6.1
A typical dew point sensor shown here is the General Eastern Model D-2.
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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.
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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.
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Figure 6.4
Note the flow meter will be removed during the calibration due to the potential condensation at the outlet tube.
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Figure 6.5
A condensate trap can be used to collect condensing moisture before the flow meter as shown in Fig 6.5.
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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.
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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.
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Figure 6.8
Using HumiCalc© calculate the actual generated dew-point using the values displayed on the 2500 screen Figure 6.8.
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Figure 6.9
DUT display at a humidity set point of 77.39 calculated dew point 34.999, test temperature of 39.71.
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Figure 6.10
Using ControLog Automation software under Mode menu tool bar select Dew Point.
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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.
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Figure 6.12
Next click on the the Dew Point Field under Control Parameters and enter 35.0 °C and Click OK.
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Figure 6.13
On the Run menu select Generate and begin the calibration test.
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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.