Super Systems Simple Dew - Manual (Page 7)

Simple Dew Digital Dew Point Analyzer Operations Manual
Super Systems Inc. Page 7 of 18
The dew point sensor is a “dielectric ceramic” that varies its electrical capacitance with
changes in relative humidity. The sensor is mounted in a short probe, which is installed in a T-
fitting that allows the sample gas to flow past the sensor. The tip of this probe contains the
dielectric ceramic relative humidity (RH) sensor, as well as a built in temperature sensor to
determine its dry bulb temperature. Information from both of these sensors is used to compute
the resultant dew point.
Maintenance/Safety Issues
Maintaining proper sensor temperature will prevent the premature failure of the sensor. The
operating temperature of the sensor should remain below 130° F (54°C) at all times. To
determine the sensor temperature, measure the voltage between pins 5(+) and 9(-) on the
microprocessor board. The voltage will be between 0 and 1VDC. Use the chart in Appendix A to
determine the temperature in °F, or use Appendix B to determine the temperature in °C. If this
temperature shows in excess of 130°F (54°C), the length of sample tubing should be increased
to allow for adequate cooling of the sample before it passes the sensor tip.
Factory Calibration
Calibration of the sensor is recommended annually. SSi’s initial calibration is performed in our
ISO/IEC 17025 certified laboratory, and includes an NIST traceable “Certificate of Calibration”.
Any calibration performed at SSi will be NIST traceable and will have documentation of ISO/IEC
17025 certification. The certificate also indicates the accuracy of the analyzer before and after
calibration. Please contact Super Systems, Inc. at (513) 772-0060 for more information
regarding this service.
Field Calibration
It is also possible to calibrate the Simple Dew in the field, which will require one of two optional
calibration kits. One calibration kit is NIST traceable (Part No. 31425); one kit is non-traceable
(Part No. 31030). To perform this calibration, you will need a calibration kit and a voltmeter that
will allow you to measure between 0 and 1 volt DC. Since there is no display on the instrument
itself, the voltages from the sensor circuit board will have to be translated into temperature and
dew point measurements for the purpose of verifying the calibration. The instructions for doing
this are contained in this document along with reference charts to aid in the interpretation of
the voltages.
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 Locate the key components within the unit
1.1 The microprocessor 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: