Tech Support Document
Thunder Support Document

Hygrometer Calibration

Edge Tech Model 650.

Figure 1.1

A typical hand held hygrometer with humidity and temperature probe Edgetech Model 650. Typical accuracy for this hygrometer is specified at ±2.0 %RH

The calibration of the hand held hygrometer as described and illustrated will be a simple 3 point calibration at 20, 50, & 80% RH at a test temperature of 23 °C.

It is always a good idea to review the operations manual for the instrument you will be calibrating.

For this calibration use the manifold accessory in the test chamber of the 2500. The manifold will thread into the chamber inlet port with a ¼ inch NPT male thread. It is not necessary to seal or tighten the manifold tight.

The manifold accessory will reduce the calibration test time.

Bundle the RH/Temp probe and the chamber temp sensor from the 2500 together in the manifold as illustrated. It is important that the RH/Temp probe from the hygrometer is positioned with the 2500 chamber temp sensor.



Insert the Manifold in the Chamber.

Figure 1.2

Position the RH/Temp probe into the manifold fixture with the 2500 chamber temperature sensor. Close the chamber door.



Insert the Foam Plug.

Figure 1.3

Seal the access port with the white foam plug, the foam plug can be drilled or cut for the probe cable.



Change the Set Point to 23 C.

Figure 1.4

Change the set point on the 2500 control screen to 20% RH at PC/TC, change the chamber temperature set point to 23 °C.



Press RUN to start the Calibration.

Figure 1.5

Press RUN to start the 2500 and begin the calibration. As a rule of thumb we will allow the 2500 system and hand held hygrometer to warm up for 60 minutes before taking our first test point. The test point interval will be 30 minutes after the initial warm up.



Thunder Cal Worksheet.

Figure 1.6

Thunder metrologists use a calibration worksheet to record data from the 2500 and the device under test. Ambient test conditions in the lab are noted and dated on the work sheet. Data collected from the 2500 will include the headings as listed in this example.



Enter 20 %RH in this Field.

Figure 1.7

ControLog® Automation software can be used in place of the manual set points as described in the previous section. Click on the %RH Set point field of the Control Parameters window, the dialog box will appear, using the keyboard enter a set point of 20 then click OK.



Enter 23 C in this Field.

Figure 1.8

Click on the Saturation Temp Set point field of the Control Parameters window, the dialog box will appear, using the keyboard enter a set point of 23 for a chamber temperature of 23 °C and then click OK.



Click RUN and select Generate.

Figure 1.9

Select Generate from the Run menu and click. When Generate mode begins, all fields on the Control Parameters window and the Calculated Humidity Values window begin to update, and the Status Log shows the time that the Generate Mode was started.



Test point at 20 %RH and 23 C.

Figure 1.10

After 60 minutes we are ready to take a test point at 20 %RH at 23 °C. Record the readings from the 2500 and hand held hygrometer. Allow extra time if the DUT is still stabilizing at the test point.



Graph at 20 %RH and 23 C.

Figure 1.11

ControLog® Automation screen in the graph mode shows a stable set point at 20 %RH and 23 °C chamber temperature.



Hand Held at 20 %RH and 23 C.

Figure 1.12

The displayed output values from the hand held hygrometer should be recorded for %RH and Temperature.



Change the Set Point to 50 %RH and 23 C.

Figure 1.13

Change the set point on the 2500 to 50 %RH at 23 °C, allow 30 minutes for the system to stabilize at the new calibration point.



Enter 50 %RH in this Field.

Figure 1.14

Click on the %RH Set point field of the Control Parameters window, the dialog box will appear, using the keyboard enter a set point of 50 then click OK, allow 30 minutes for the system to stabilize at the new calibration point.



Test point at 50 %RH and 23 C.

Figure 1.15

After 30 minutes we are ready to take a test point at 50 %RH at 23 °C. Record the readings from the 2500 and hand held hygrometer. Allow extra time if the DUT is still stabilizing at the test point.



Graph at 50 %RH and 23 C.

Figure 1.16

ControLog® Automation screen in the graph mode shows a stable set point at 50 %RH and 23 °C chamber temperature.



Hand Held at 50 %RH and 23 C.

Figure 1.17

The displayed output values from the hand held hygrometer should be recorded for %RH and Temperature, allow extra time if the DUT is still stabilizing.



Change the Set Point to 80 %RH and 23 C.

Figure 1.18

Change the set point on the 2500 to 80 %RH at 23 °C, allow 30 minutes for the system to stabilize at the new calibration point.



Enter 80 %RH in this Field.

Figure 1.19

Click on the %RH Set point field of the Control Parameters window, the dialog box will appear, using the keyboard enter a set point of 80 then click OK, allow 30 minutes for the system to stabilize at the new calibration point.



Test point at 80 %RH and 23 C.

Figure 1.20

After 30 minutes we are ready to take a test point at 80 %RH at 23 °C. Record the readings from the 2500 and hand held hygrometer. Allow extra time if the DUT is still stabilizing at the test point.



Graph at 80 %RH and 23 C.

Figure 1.21

ControLog® Automation screen in the graph mode shows a stable set point at 80 %RH and 23 °C chamber temperature.



Hand Held at 80 %RH and 23 C.

Figure 1.22

Record the final test point from the DUT display for %RH and Temperature.

Press Stop on the 2500 keyboard or, Select Shutdown from the Run menu, once the 2500 generator is shut down the system will prompt you to save the system data, which was acquired during this calibration

The initial as found calibration is complete. The filter element or screen that protects the humidity sensor element should be cleaned and inspected as per the manufacturers recommendation before calibration adjustment and testing the as left calibration of the hand held hygrometer.

The as left calibration should be performed at the same test temperature of 23 °C using the same 3 test points beginning at 20 %RH, test point interval will be 30 minutes.


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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