Model IR5500
55
8.0 Appendix A
8.1 Split-Range Analog Output Option
NOTE:
This section is intended to be read and understood by a systems integration
engineer. It is not necessary to understand this in order to safely use the Model
IR5500 gas detector. The split-range analog output option is turned off by default
and should be left off unless you are certain the control room PLC is properly
configured.
If the split-range mode is turned on and the PLC is not set to calculate the analog
output this way, the system will fail-to-safe because the analog is interpreted as
representing a higher concentration than is present. This may cause the PLC to
falsely indicate alarms.
The IR5500 can be set through the SE menu to operate in split-range analog output mode.
This mode gives the advantages of very high sensitivity of the ppm
·
m range and the full
range detection of the LEL
·
m scale. The analog output range from 4 to 20 mA is split so that
values from 4 to 12 mA represent 0 – 5,000 ppm
·
m and values from 12 to 20 mA represent 0
– 5.0 LEL
·
m.
For the heavy hydrocarbon version of the Model IR5500 detector the ranges are 4 to 12 mA
represent 0 – 2,000 ppm
·
m and values from 12 to 20 mA represent 0 – 1 LEL
·
m.
This mode is intended for use with a PLC which will convert the analog current back to both
ppm
·
m and LEL
·
m readings.
The conversion equations for the PLC are:
ppm
·
m % F.S. = (Analog Output – 4.00) / 0.08
LEL
·
m % F.S. = (Analog Output – 12.0) / 0.08
where Analog Output is the current measured by the PLC in units of mA.
To display the value in ppm
·
m or LEL
·
m the following conversion should be used:
Methane detectors
ppm
·
m = ppm
·
m % F.S. * 50
LEL
·
m = LEL
·
m % F.S. / 20
Propane detectors
ppm
·
m = ppm
·
m % F.S. * 20
LEL
·
m = LEL
·
m % F.S. / 100