Detcon PI-700 - Manual (Page 31)

Model PI-700
PI-700 Instruction Manual Rev. 2.5 Page 27 of 54
4. RS-485 Modbus™ Protocol
Model DM-700 sensors feature Modbus™ compatible communications protocol and are addressable via the
program mode. Other protocols are available. Contact the Detcon factory for specific protocol requirements.
Communication is two wire, half duplex 485, 9600 baud, 8 data bits, 1 stop bit, no parity, with the sensor set
up as a slave device. A master controller up to 4000 feet away can theoretically poll up to 256 different
sensors. This number may not be realistic in harsh environments where noise and/or wiring conditions would
make it impractical to place so many devices on the same pair of wires. If a multi-point system is being
utilized, each sensor should be set for a different address. Typical address settings are: 01, 02, 03, 04, 05, 06,
07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11…etc.
Sensor RS-485 ID numbers are factory default to 01. These can be changed in the field via the Operator
Interface described in Section 3.5.5 Set Serial ID.
The following section explains the details of the Modbus™ protocol that the DM-700 sensor supports.
Code 03 - Read Holding Registers is the only code supported by the transmitter. Each transmitter contains 6
holding registers which reflect its current status.
Table 3 Modbus™ Registers
FC REG Content Description R/W Content Definition
Value Meaning Range
03 40000 Device Type R 8 700 Sensor
03
06 40001
40001 Read Detectable
Range 1,2
Write Detectable Range
R/W 100
10000 For 0-100
For 0-10000
2
DM – 0 to 10000
FP – Read only
TP – 20, 50, 100, 200
IR – 0 to 10000
PI – 0 to 10000
03 40002 Read Concentration 3,2 R 1000 Bound by range. If > range, this
value is in fault.
03
06 40003
40003 Read AutoSpan Level 4,2
Write AutoSpan Level
R/W 50 Span gas at 50 DM – 1% to 95% of Range (40001)
FP – 5% to 95% of Range (40001)
TP – 2% to 50% of Range (40001)
IR – 5% to 95% of Range (40001)
PI – 1% to 95% of Range (40001)
03 40004 Read Sensor Life R 85 For 85% sensor life
03 40005 Read Fault Status Bits 5 R 0x0001
0x0002
0x0004
0x0008
0x0010
0x0020
0x0040
0x0080
0x0100
0x0200
0x0400
0x0800
0x1000
0x2000
0x4000
0x8000 Global Fault
Auto Span Fault
Temperature Fault
4-20mA Fault
Input Voltage Fault
Memory Fault
Processor Fault
Clearing Fault
Stability Fault
Range Fault
Sensor Fault
Zero Fault
Sensor Fault 2
In Calibration
Communication Error
03 40006 Read Model # R 1, 2, 3, 4, 5 DM, FP, IR, TP, PID
respectively
03 40007 Read Days Since Cal R 29 29days
03 40008 4-20 Current Output
mA x100
R 400 4.00mA Range
03 40009 Read Input Voltage
V x100
R 2400 24.00V
03 40010 Read Temperature R 28 28 °C
03/
06
40011 Special #1 R/W Function dependent on value of
40006 (See Special Register
Table 4)