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1.5 Output signal
Depending on the needs of the user, the gas detector can work with the output circuit configured as:
RS-485 output
this is the basic solution recommended by the manufacturer. It allows easy integration with data
transmission systems, visualization systems in ACP, industrial controllers. Gas detector with this
type of output are marked with 485.
• Communication through RS-485 interface is implemented according to MODBUS ASCII
(SmArtGas 3) and SigmaBus (Sigma SmArt). Applications of other protocols are also possible.
• For gas detectors with RS485 output, the output signal is digitized. In general, the gas detector
status is described by the following variables:
∘ the measurement result in a percentage range (number 0 – 100.00%),
∘
information of exceeding the alarm thresholds,
∘ status words with information about failures, etc.
4 – 20 output (applies to SmArtGas 3)
• standard current signal 4 – 20 mA
It allows for easy integration of the gas detectors with other automation systems, e.g. with
industrial controllers. Gas detectors with this type of output are marked with 4 – 20,
• values below 4 mA correspond to states of faulty of the sensor (see appendix [13]),
• 4 mA corresponds to zero concentration of the measured gas,
• 20 mA corresponds to the concentration corresponding to the declared scope of operation of
the gas detector (see appendix [2]) or higher concentrations (saturation of the gas detector),
• current value for a particular concentration can be calculated with the following formula:
I = 4 mA + 16 mA *
concentration of gas applied to the gas detector
gas detector measuring range
contact output (applies to SmArtGas 3)
it allows the direct use of gas detectors to control executive devices. Detectors with this type of
output are marked with CON.
There are three contact signals which may be used, e.g. in the following way:
• PK1: Warning 1,
• PK2: Alarm,
• PK3: Gas detector failure.
PK output parameters are described in table 7.
p. 9|34
User's Manual: POD-009-ENG R07