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GasCheck
Operating Manual V2.4
9
4.
USING THE OUTPUT
4.1 A
Linearisation of the GasCheck
The absorption of infrared energy by a gas is non-linear and therefore the
output from the sensor is also non-linear.
The output volts as a function of gas concentration for the various ranges are
given in Appendices 1- 3. This may be used to set a trigger or alarm level
corresponding to a particular gas concentration.
The output may be linearised using a segmented linearisation technique in
which the linearisation curve is approximated to a series of straight lines. This
may be achieved, with negligible errors, using the data given in Appendices 1
- 3. Note that the transmitter must always be separately calibrated at zero and
span despite this linearisation.
4.1 B
Output options for the GasCheck with linearisation
The sensor is supplied configured for a 4-20mA current output with a fault
state being indicated by 0mA. Alternative current/voltage outputs are
available by changing links on the board and fitting a resistor (voltage outputs
only).
To change the output from 4-20mA to 0-20mA, the link on LK1 should be
removed and fitted to LK2.
To disable the function, which forces the output to 0mA in the event of the
failure of the sensor head, remove LK3.
To provide a voltage output, the current output should be configured as a 0 -
20mA output (see above) and appropriate resistors should be fitted to
positions R36/R37 on the PCB. The output is generated by passing the output
current through the parallel combination of R36 and R37. Table 1 gives
typical resistance combinations for voltage outputs.
Required Voltage Output
Resistor Values (R36 and R37)
0 - 1V
fit 2 x 100
0 - 3V
fit 2 x 300
0 - 5V
fit 2 x 500
0 - 10V
fit 2 x 1k
TABLE 1