RKI Instruments 65-2424RK - Manual (Page 15)

65-2424RK H
2
S Transmitter • 11
15. Calibrate the H
2
S transmitter as described in the Calibration section of this insert.
Calibration Frequency
Although there is no particular calibration frequency that is correct for all applications, a
calibration frequency of every 3 to 6 months is adequate for most H
2
S transmitter
applications. Unless experience in a particular application dictates otherwise, RKI
Instruments, Inc. recommends a calibration frequency of every 3 months.
If an application is not very demanding, for example detection in a clean, temperature
controlled environment where H
2
S is not normally present and calibration adjustments
are minimal at calibration, then a calibration frequency of every 6 months is adequate.
If an application is very demanding, for example if H
2
S is present often and in significant
concentrations or the environment is not well controlled, then more frequent calibration
than every 3 months may be necessary.
Calibration
This section describes how to calibrate the H
2
S transmitter. It includes procedures to
prepare for calibration, set the zero reading, set the response reading, and return to
normal operation. It describes the test using a calibration kit that includes a calibration
cup, calibration gas, sample tubing, and a fixed flow regulator with an on/off knob. RKI
Instruments, Inc. recommends using a 0.5 LPM (liters per minute) fixed flow regulator.
Preparing for Calibration
NOTE: Calibrating the H
2
S transmitter may cause alarms. Be sure to put the controller
into its calibration program or disable external alarms before calibrating.
1. Screw the regulator into the zero air calibration cylinder.
2. Use the calibration kit sample tubing to connect the regulator to the calibration cup.
3. Set a voltmeter to measure in the millivolt (mV) range.
4. Remove the enclosure cover, then plug the voltmeter leads into the test points on the
amplifier PCB.
Plug the positive lead into the test point labeled CAL+; plug the negative lead into the
test point labeled CAL-.
5. Use the following formula to determine the correct test points output for the
calibrating sample.
Output (mV) = (calibrating sample/fullscale) X 400 + 100
For example, with a calibrating sample of 25 PPM H
2
S and a fullscale setting of
100 PPM, the correct output is 200 mV.
200 (mV) = (25/100) X 400 +100