1.13
1.7.2 Data Output Board 01100927
A data output board may be fitted. The board uses an ASCII transmission code operating an
asynchronous signal with a start bit, eight data bits and two stop bits at a transmission rate of
300 baud.
Two types of output are available from the board. The first switches a 20 mA current loop
signal to allow maximum cable length from the Control unit . Secondly, the data may be
transmitted as a bipolar RS 232C type signal for interfacing to a local computer terminal.
Full details of the protocol of the digital data output is given in Appendix 4.
1.7.3 Pressure Compensation 01100997B
Pressure compensation is an option which should be specified at the time of ordering. It cannot
be fitted in the field.
The 1161 dry gas sample panel should be fitted if pressure compensation is specified as this
has facilities for calibrating the pressure compensation option.
The pressure transducer measures the pressure inside the measuring cell and provides an
output which is used by the microprocessor to compensate for changes in pressure to ensure
that the oxygen concentration reading remains constant for fluctuations in sample pressure.
NOTE: The pressure in the cell should be within the range 83 to 124kPa absolute (12 to
18 psia).
If the sample is vented to atmosphere the reading will be compensated for changes in
barometric pressure. This arrangement is recommended for very critical applications,
particularly when samples with a high oxygen content are being measured (e.g. in oxygen
purity monitoring), when normal atmospheric pressure variations could represent a significant
change in the reading.
If the sample is being returned to process then pressure compensation may be required to
compensate for possible fluctuations in process pressure.
Note that in order to calibrate the pressure compensation it is necessary to use a calibrating
gas with a high oxygen content. If the sample is being returned to process it may be necessary
to fit stream selector valves to the exhaust of the analyser so that calibrating gases are vented
to atmosphere.
The dry gas sampling system type 1161 has facilities for calibrating the pressure
compensation. It is suggested that this should always be used with pressure compensation.
On systems with separated Transducer and Control (or Interface) units with pressure
compensation fitted the cable length should not exceed 30m (100ft). The performance will be
degraded if the cable length is between 30 and 100m.
Pressure compensation is not available for analysers fitted with the 1162 wet gas sampling
system or with the model 1132 Transducer unit.
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