17
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-Rover 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. 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-Rover. 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-Rover.
A-CAL Operation.
Calibrate the thermal conductivity sensor with methane or natural
gas first, and then calibrate the CO and catalytic combustion sensors with 2.5% methane and 100
ppm CO in air. Alternatively, use the One-Gas calibration algorithm and calibrate the CO and
catalytic combustion sensors with 2.5% methane and 100 ppm CO in air.
A-CAL Calibration with Pure Methane or System Gas.
Power on the Gas-Rover with
the left “Power-On” button and while the unit displays “
Calibrate By …..
” press the “CAL button.
After autozero, choose “A-CAL”, connect pure methane or natural gas and press the left “Yes”
button. 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.
Calibration with 2.5% Methane and 100 ppm CO.
Power on the Gas-Rover with the
left “Power-On” button and while the unit displays “
Calibrate By …..
” press the right “CAL”
button once. After a successful autozero, choose A-CAL. With the unit’s screen displaying
“
Connect Calibration Gas
”, connect the 2.5% methane and 100 ppm CO in air calibration gas and
press the left “Yes” button. The screen displays “
Calibrating
” for about a minute and then changes
to “
Calibration OK
” with a display of % GAS (and ppm CO readings if it has a CO sensor) or
“
Does Not Calibrate
”, if calibration was unsuccessful. Pressing the left “Re-Try” button returns
to the Calibration screen. If three tries at calibration are unsuccessful, 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 Survey mode, the second (mw/1%) to the
Monitor mode. If the sensitivity of the Survey mode falls below 0.5 µw/ppm, the natural gas
sensor should be changed. Similarly if the sensitivity in the Monitor mode falls below 8 mw/1%
GAS, the gas sensor should be changed. In both cases the display reads
“Please Change Methane
Sensor”
and the instrument is placed in Off condition until a new sensor is installed.
PART 3. THE USB INTERFACE
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.
