50 M2A Transmitter Operator’s Manual
Calibration Frequency
Some M2As have IR (infrared) type detectors, such as an M2A for CO
2
or an LEL M2A with an IR detector.
Most of the M2As do not have an IR detector. For example, an H
2
S M2A has an electrochemical detector and
some of the combustible M2As use catalytic detectors. The M2As that use IR detectors typically need less
frequent calibration as is discussed below. See Table 3, “Infrared (IR) Detectors,” on page 12 to see which M2As
are IR versions.
Although there is no particular calibration frequency that is correct for all applications, a calibration frequency of
every 3 to 6 months for M2As that do not have an IR detector and every 6 to 12 months for M2As that have an IR
detector is adequate for most M2A applications. Unless experience in a particular application dictates otherwise,
RKI Instruments, Inc. recommends a calibration frequency of every 3 months for M2As that do not have an IR
detector and every 6 months for M2As that have an IR detector.
If an application is not very demanding, for example detection in a clean, temperature controlled environment
where the toxic or combustible target gas is not normally present, and calibration adjustments are minimal at
calibration, then a calibration frequency of every 6 months for a non-IR M2A or 12 months for an IR M2A is
adequate.
If an application is very demanding, for example if a combustible or toxic gas is present often and in significant
concentrations or the environment is not well controlled, then more frequent calibration than every 3 months for
a non-IR M2A or every 6 months for an IR M2A may be necessary. For combustible gas detection with an M2A
that uses a catalytic detector, if potential catalyst poisons are known or likely to be present, more frequent
calibration than every 3 months will be necessary.
Calibration, Combustible Gas, CO
2
, and Toxic Versions
This section describes how to calibrate the combustible gas, CO
2
, and toxic gas versions of the M2A. It includes
procedures to prepare for calibration, enter Calibration Mode, adjust the fresh air (zero) setting, adjust the span
setting, and return to normal operation. See the next section, “Calibration, Oxygen Version” for instructions to
calibrate an oxygen M2A.
NOTE: The detector must be calibrated with a gas concentration between 10% and 100% of the channel’s
full scale value (ie. a 0 - 300 ppm CO detector must be calibrated with a CO concentration between
30 and 300 ppm).
WARNING: The M2A is not an active gas monitoring device during the calibration procedure. The 4-20
mA output signal will “freeze” at 3.5 mA and all relays will remain in their non-alarm state
while the M2A is in Calibration Mode. The output signal will not indicate current readings
and the relays will not resume operating normally until the M2A is in normal operation
again.
Special Note About Calibrating a ClO
2
Detector
RKI Instruments, Inc. recommends using a ClO
2
generator to set the ClO
2
detector’s response reading. The flow
rate on the generator needs to be set to 0.5 LPM and RKI Instruments, Inc. recommends that 0.5 ppm ClO
2
be
used. If a ClO
2
generator is used for calibration, the steps related to the use of a calibration gas cylinder in the
instructions below can be disregarded.
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