Land 4500 MKII Premier, Operation And Maintenance Manual

Page: 61 / 139

Model 4500 Premier Dust and Opacity Monitor
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Protocol Format
The Model 4500 Premier utilises the MODBUS RTU (Remote Terminal Unit) transmission format.
Serial communications are fixed at 1 start bit, 8 data bits, no parity, 1 stop bit, and the data rate is
fixed at 9600 baud. The following are examples of master query and slave response messages in
RTU format, polling slave address 11 (hex).
(03) Read Register(s)
Query Response
Slave Address 11 Slave Address 11
Function 03 Function 03
Register Address Hi 00 Byte Count 06
Register Address Lo 20 Data 1 Hi xx
No. of Registers Hi 00 Data 1 Lo xx
No. of Registers Lo 03 Data 2 Hi xx
CRC Hi xx Data 2 Lo xx
CRC Lo xx Data 3 Hi xx
Data 3 Lo xx
CRC Hi xx
CRC Lo xx
Calibration Phases (Register 168)
Three bits in this register are defined: all other bits are zero. If one bit is true then the others are false.
Bit 0 Zero Phase
True during a Calibration Check sequence.
Goes true Cal Action delay seconds before the zero reflector starts to drive in.
Goes false before the upscale filter starts to drive in.
Bit 1 Span Phase
True during Calibration Check sequence.
Goes true Cal Action Delay seconds before the upscale filter starts to drive in (ie simultaneously with
Bit 0 going false)
Goes false Cal Action Delay seconds before the zero reflector and upscale filter start to drive out.
Bit 2 Audit Phase
True throughout any Calibration Audit operation.
Goes true Cal Action Delay seconds before the zero reflector starts to drive in.
Goes false Cal Action Delay seconds before the zero reflector starts to drive out.