RKI Instruments 65-2391RK User Manual
Page 11
65-2391RK CO
2
Transmitter • 7
NOTE:
When first powered up, the transmitter will enter about a one minute period
when the 4-20 mA output is stabilizing and may be above the controller alarm
points or well below zero momentarily. RKI controllers have a one minute
warmup period when the controller does not display any gas reading or give any
alarm indication. The CO
2
transmitter’s 4-20 mA signal should be stable by the
time the controller’s warmup period is over.
CAUTION:
Allow the detector to warm up for 5 minutes before you continue with the next
section, “Setting the Zero Signal”.
Setting the Zero Signal
Since there is a background of CO
2
in air of typically 300 - 600 ppm (0.03 - 0.06 %volume),
it is necessary to use a calibration kit with a 100% nitrogen cylinder to set the zero signal of
a CO
2
transmitter with a low range detector. Fresh air can be used to zero the transmitter
if a 0-50 %volume or 0-100 %volume detector is being used.
NOTE:
The following procedure assumes the use of a calibration kit which includes a
100% nitrogen calibration gas cylinder, a 0.5 LPM fixed flow regulator with an
on/off knob, a calibration cup for the detector, and a short piece of sample tubing
to connect the regulator to the calibration cup.
1.
Place the controller into its calibration program or disable external alarms to avoid
accidental alarms during the zero setting procedure.
2.
Screw the calibration cup onto the bottom of the detector.
3.
Use the sample tubing that comes with the calibration kit to connect the regulator to
the calibration cup.
4.
Set a voltmeter to measure in the millivolt (mV) range.
5.
Remove the junction box cover, then plug the voltmeter leads into the test points on
the amplifier.
Plug the positive lead into the test point labeled TP+; plug the negative lead into the
test point labeled TP-.
6.
Screw the regulator into the 100% nitrogen calibration cylinder.
7.
Turn the regulator knob counterclockwise to open the regulator.
8.
Allow the gas to flow for one minute and verify a reading of 100 mV (±2 mV). If
necessary, use the zero potentiometer on the amplifier to adjust the reading to 100 mV
(±2 mV).
9.
Turn the regulator knob clockwise to close the regulator.
10. Unscrew the regulator from the 100% nitrogen calibration cylinder.
11. Unscrew the calibration cup from the detector.
12. Reinstall the junction box cover.
13. Return the controller to normal operation or enable external alarms.