Sierra Monitor Corporation Gas Detector User Manual

 

 

1 

All Registers are MODBUS 16 bit registers 

2 

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

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

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

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

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

2.5  Control 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. 

3 

Where 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.  

4 

Some 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” 

5 

Registers 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