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3.
CALIBRATION
Calibration must be carried out on a new sensor the next time the instrument is turned on;
with an already installed sensor, the calibration should be carried out at specified intervals. The A-
CAL firmware calibrates the Gas-Explorer using calibration gas available from Bascom-Turner
containing 2.5 + 0.05% methane and 100 ppm + 2 ppm CO in air. Calibration gas is provided in a
disposable tank containing either 105 liters of gas (Part No. MC-105) or 620 liters (part No. MC-
620). The thermal conductivity sensor is automatically calibrated for 100% methane during the
autozero routine preceding calibration with the One-Gas calibration algorithm. It can be also
calibrated with pure methane or system gas by using the Two-Gas calibration. The oxygen sensor
is calibrated with ambient air during power-up.
The calibration gas must be delivered at or near atmospheric pressure to ensure accurate
calibration. For the 105 liter gas tanks, Bascom-Turner recommends using a constant flow
regulator (Part No. FR-001) set to the sampling rate of the Gas-Explorer. For the 620 liter gas
tanks, Bascom-Turner recommends using an on-demand regulator (Part No. FR-401), which
automatically adjusts its flow to the pumping rate of the Gas-Explorer.
A-CAL Calibration. The A-CAL procedure guides the user through the calibration
procedure and instructs when to supply the required gases. After the Autozero is successful, the
user can select a One-Gas calibration which only uses the 2.5% Methane with 100 ppm CO or the
Two-Gas calibration which uses both the 2.5% Methane with 100 ppm CO and Pure Methane or
System Gas. The Two-Gas procedure should be utilized when it is necessary for the System Gas
to report as 100% Gas such as when purging pipes.
When the gases have been connected, the screen displays "Calibrating" for about a minute
and then changes to "Calibration OK" with a display of readings taken while sampling calibration
gas or "Does Not Calibrate" if calibration was unsuccessful. Three tries are allowed before the
screen displays "Please Service" for 15 seconds and then the instrument turns OFF.
Following calibration, an intermediate screen displays the sensitivity in µw/ppm and
mw/1%. The first quantity (µw/ppm) refers to the Track Gas mode, the second (mw/1%) to the
Monitor mode. If the sensitivity of the Track Gas mode falls below 0.5 µw/ppm, the gas sensor
should be changed. Similarly if the sensitivity in the Monitor mode falls below 8 mw/1%, the gas
sensor should be changed. In both cases, the display reads "Please Change Methane Sensor" and
the instrument is not operable until a new sensor is installed.
Calibration of the H
calibration gas (10ppm H
conductivity sensor as well as the H
CAUTION: Automatic calibration presupposes and depends on using Bascom-Turner's
calibration gas (Part No. MC-105 or MC-620). Do not use a gas of a different
composition for automatic calibration.
S sensor. Proceed as above for pure methane, but use the H
2
S in methane). The instrument will automatically calibrate the thermal
2
S sensor.
2
18
S
2
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