FIELD CALIBRATION –
It is also possible to calibrate the DP2000 in the field, which will require the optional calibration kit (Part Number 31030). The instructions for a field calibration are shown here, however please feel free to contact Super Systems at 513-772-0060 if you would like to review the process with us before you begin.
The calibration kit consists of two bottles of saturated salt solution in which each bottle generates a precise relative humidity percentage (R.H. %) value. One bottle is 11.3% R.H., and the other is 75.3% R.H. These two specific calibration points are already pre-programmed into the microprocessor board.
1.0 Open the unit
1.1 Remove the aluminum faceplate of the DP2000 by removing the single allen-head cap screw located at the bottom front of the faceplate. After the screw has been removed, carefully lift the front of the faceplate and slide it towards you about an inch. After the faceplate has been removed, it can temporarily be rested in the lid of the open case, to allow access to the components inside. This plate will still be connected to the interior circuit boards, so care should be taken to maintain all existing connections.
2.0 Locate the key components within the unit
2.1 The microprocessor board is located in the front left side of the unit. This board contains three very small buttons that are used for calibration. Two are next to one another, and they are marked “75.3%” and “11.3%”, while the other has no label. The unmarked button is the “Calibrate” button. The approximate locations of each button are shown on this diagram:
2.2 The sensor-sampling chamber is located in the back left of the unit. It is the gray rectangular box with brass barb fittings on either side with a black plastic gland protruding from the center.
2.3 The sensor probe is positioned in the sensor-sampling chamber. It is held in place by the nut on the black plastic gland.
3.0 Remove the sensor probe from the sensor sampling chamber.
3.1 Loosen the black plastic gland nut and slowly slide the sensor probe out through the airtight seal. Care must be taken when removing this sensor probe, since the tip is very delicate and can be easily damaged if it is mishandled. Note that the probe has white mark at the wire entry point, which must be aligned with corresponding white mark in plastic gland when it is re-inserted in the sampling chamber.
4.0 Install the sensor probe into the 75.3% salt solution.
4.1 Slip the black sensor gland (supplied in the calibration kit) over the sensor probe with the sensor tip protruding from the threaded end of the gland and the sensor wires being flush with the top of the rubber o-ring in the gland. Tighten the gland around the sensor. This does not need to be done with a wrench or other tools, but it does need to be tight enough to prevent ambient air from contaminating the humidity level of the sampling chamber.
4.2 Remove the cap of the 75.3% salt solution and install the sensor gland (with the sensor) into the salt solution. To increase the life of the calibration salts, an effort should be made to minimize the amount of time that the salt solution is exposed to the ambient air.
5.0 Allow the sensor to reach equilibrium with the calibration salt.
5.1 With the power to the unit still turned off, leave the sensor in the calibration salt for a minimum of eighteen (18) hours. It is acceptable to leave the sensor in the salt solution for a longer period of time, even a few days, if desired.
6.0 Begin the 75.3% (Span) calibration process.
6.1 After leaving the sensor in the salt for at least eighteen (18) hours, turn the unit on. The reading on the display is not important at this point.
6.2 Simultaneously press the “75.3%” and “Calibration” buttons on the microprocessor board.
7.0 Verify the 75.3% (Span) calibration.
7.1 Do not be concerned if the unit does not display 75.3, since it is not supposed to match the value of the calibration salt.
7.2 Use the “Sensor Temp” switch on the faceplate of the unit to determine and record the sensor temperature.
7.3 Look up this temperature on the “Theoretical Dew Point Values for Calibration Verification” chart located in the back of this manual. Appendix “A” will show the temperature values in Fahrenheit, and Appendix B will show the temperature values in Celsius.
7.4 Next to the appropriate temperature, note the number in the corresponding column titled “75.3%”. This should match with the dew point that is shown on the display of the DP2000.
8.0 Determine the acceptability of the reading.
8.1 The value printed on the chart in Appendix A is a theoretical value, and some variation can be expected. When a calibration is performed at SSI, we certify (in writing) that the unit displays within +/- 1 degree of the theoretical value after it has been calibrated. We would not consider a calibration to be successful unless it is within +/- 1 degree, however in the case of a field calibration, this degree of accuracy may or may not be required. The degree of accuracy that is acceptable is determined by the policy of the person performing the calibration.
NOTE: Keep in mind that the DP2000 only displays even numbers, and not tenths of a degree. Therefore, a reading of 65°F could be as low as 64.50 or as high as 65.49.
9.0 Allow the sensor to achieve equilibrium at ambient atmosphere.
9.1 After the 75.3% (Span) calibration has been completed, remove the sensor from the calibration salt and replace the cap on the salt.
9.2 Leave the sensor probe in the gland and while the unit is still on, allow it to achieve equilibrium at the ambient atmosphere in the room. This is accomplished by simply leaving the sensor exposed to ambient air for between two and three minutes. You will know when this has been accomplished when the numbers on the display begin to stabilize.
10.0 Install the sensor probe into the 11.3% salt solution.
10.1 Remove the cap of the 11.3% salt solution and install the sensor gland (with the sensor) into the salt solution. To increase the life of the calibration salts, an effort should be made to minimize the amount of time that the salt solution is exposed to the ambient air.
10.2 Turn the unit off.
11.0 Allow the sensor to reach equilibrium with the calibration salt.
11.1 With the power to the unit still turned off, leave the sensor in the calibration salt for a minimum of 24 hours. It is acceptable to leave the sensor in the salt solution for a longer period of time, even a few days, if desired.
12.0 Begin the 11.3% (Zero) calibration process
12.1 After leaving the sensor in the salt for at least twenty-four (24) hours, turn the unit on. The reading on the display is not important at this point.
12.2 Simultaneously press the “11.3%” and “Calibration” buttons on the microprocessor board.
13.0 Verify the 11.3% (Zero) calibration
13.1 Do not be concerned if the unit does not display 11.3, since it is not supposed to match the value of the calibration salt.
13.2 Use the “Sensor Temp” switch on the faceplate of the unit to determine and record the sensor temperature.
13.3 Look up this temperature on the “Theoretical Dew Point Values for Calibration Verification” chart located in the back of this manual. Appendix “A” will show the temperature values in Fahrenheit, and Appendix B will show the temperature values in Celsius.
13.4 Next to the appropriate temperature, note the number in the corresponding column titled “11.3%”. This should match with the dew point that is shown on the display of the DP2000.
14.0 Determine the acceptability of the reading
14.1 The value printed on the chart in Appendix A is a theoretical value, and some variation can be expected. When a calibration is performed at SSI, we certify (in writing) that the unit displays within +/- 1 degree of the theoretical value after it has been calibrated. We would not consider a calibration to be successful unless it is within +/- 1 degree, however in the case of a field calibration, this degree of accuracy may or may not be required. The degree of accuracy that is acceptable is determined by the policy of the person performing the calibration.
NOTE: Keep in mind that the DP2000 only displays even numbers, and not tenths of a degree. Therefore, a reading of 18°F (-7.8°C) could be as low as 17.50°F (-8.06°C) or as high as 18.49°F (-7.51°C).
15.0 Allow the sensor to achieve equilibrium at ambient atmosphere
15.1 After the 11.3% (Zero) calibration has been completed, remove the sensor from the calibration salt and replace the cap.
15.2 Leave the sensor probe in the gland and while the unit is still on, allow it to achieve equilibrium at the ambient atmosphere in the room. This should take between two and three minutes. You will know when this has been accomplished when the numbers on the display begin to stabilize.
16.0 Re-assemble the unit
16.1 After the calibration process has been completed, remove the sensor probe from the gland and return it to the sensor-sampling chamber, taking care to position it properly. The white mark on the sensor probe should face towards the right of the sensor-sampling chamber (at 3:00 if it were the face of a clock.). If the white mark is not visible, then it should be placed so the sample flow directly strikes the face of the mirror on the sensor tip (the sample flows from right-to-left). In other words, the mirror should face the incoming gas stream.
16.2 Hand-tighten the black sensor gland to prevent air from leaking out of the sampling chamber.
16.3 Slide the faceplate into position with the back posts going into the corresponding holes as the faceplate slides back.
16.4 Verify that the system is leak proof by turning on the pump and placing a finger over the sample inlet port. The flow meter on the side of the unit will drop to zero if there are no leaks. If a leak is detected, make sure that all tubing connections are tight, especially the black sensor gland.
16.5 After the unit has passed the leak test, re-fasten the screw into the faceplate and tighten it.
17.0 Make sure that all caps are replaced on the calibration salts, and return the DP2000 to service.