Sierra Monitor Corporation Gas Detector specification

Sentry MODBUS I/O Memory Map

Sentry Controller

MODBUS Memory Map

Detail

1All Registers are MODBUS 16 bit registers

2There are five different ways of using MODBUS registers (see italic reference number in left column for each address)

2.1As an Analog Value: In most cases these values are scaled by multiplying by 10.

2.2As eight packed digital states, packed into one register. In this case the remaining 8 bits are unused.

2.3As a digital state where the register value can only be “0” or “1”.

2.4As a computed value, such as where “0” = no alarm, “1” = low alarm, “2” = high alarm.

2.5Control registers, where the SCADA host can write a value, such as alarm reset to the Sentry, or to set calibration concentration, or alarm set point. Note that these registers are read or write.

3Where a series of registers apply only to sensor number 1, the following sequences for sensors 2, through 8 are only referenced by the first applicable register number.

4Some values can be found in more than one place in different formats. For example when Sensor Number 6 is in high alarm and latched:

• Register 40001:5 is the bit which indicates present alarm condition.

• Register 40007:5 is the bit which indicate a latched condition, regardless of the present sensor reading (until reset)

• Register 40466 is a computed value of “2”

5Registers starting at 40224 provide the raw data read from each of the eight sensors. The following describes the data for sensor 1, the remaining registers through 40463 are for sensors 2 through 8:

40224	Sensor 1 Input Value - Multiplex 0		– V0 (Reference value of 0 volts)	0 - 6553.5
40225	Sensor 1 Input Value - Multiplex 1		– Vsignal (Current sensor signal)	0 - 6553.5
40226	Sensor 1 Input Value - Multiplex 2		– CH2 (Auxiliary data by type)	0 - 6553.5
40227	Sensor 1 Input Value - Multiplex 3		– CH3(Auxiliary data by type)	0 - 6553.5
40228	Sensor 1 Input Value - Multiplex 4		– Type	0 - 6553.5
40229	Sensor 1	Input Value - Multiplex 5 – Vin (Channel voltage)		0 - 6553.5
40230	Sensor 1	Input Value - Multiplex 6	– Calibration Switch Position (0=On)	0 - 6553.5
40231	Sensor 1	Input Value - Multiplex 7	– Vref (Reference value of 2.5 volts)	0 - 6553.5
40232	Sensor 1 Calibration Due Days

To calculate the raw signal voltage (for example), since we know Vref :

V = (Vsignal – V0) / (Vref – V0) * 2.5v

March 4, 2005

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Gas Detector specifications

Sierra Monitor Corporation, a leader in environmental monitoring and gas detection systems, has developed an innovative range of gas detectors tailored for industrial applications. These systems are designed to provide reliable, real-time monitoring of hazardous gases, ensuring the safety of personnel and the environment.

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