STATUS SCIENTIFIC CONTROLS
Installation, Commissioning & Routine Gas Testing
FGD10A-M Gas Detector
TD18/032
Issue:
10
Change Note:
1869
Page 74
LOGICAL
ADDRESS
(R/W)
DATA
TYPE
DESCRIPTION
40351
R/W
uINT16
Set Latched Relays
0x0000 = NO latched alarm function
0x0001 = latched alarm ACTIVE
Note: If Set Latched Relays is disabled during a Latched Alarm condition, the
Latched Alarm must still be reset via register
40350
10.3. Modbus Programming examples:
10.3.1. Example 1: Read Gas Level command.
Mitsubishi FX3U PLC ladder diagram:
Read Gas Level from FGD10AM at Modbus Address 1 when 50% LEL
calibration gas is present. Numbers in blue are actual monitored PLC
register values
0
M2
101 50
─[= D300 K0 ]──| |──[ADPRW H1 H3 D302 K1 D0]──
M8029
──| |────────────[SET M2]─
Explanation:
PLC register D300 is assigned as the step control register. The value here
determines which part of the overall ladder sequence is executed in which
order. In this case, “Read gas level” was assigned a step sequence value of
0 (k0 in FX3U syntax).
Flag M2 is assigned as “Modbus command in progress”
ADPRW is the special Modbus read/write command for the FX3U Modbus
interface module.
M8029 flag is th
e FX3U “modbus command complete” which stays turns on
when the modbus command is complete.
H1 is the modbus address FGD10A in hexadecimal.
H3 is the modbus “read register command” in hexadecimal.
K1 is the number of bytes to be read i.e. 1 in this case.
D302 contains the physical address of the modbus register to read in
hexadecimal. In this case 101 decimal. This equates to logical address
