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using modbus devices

A convenient solution is to use a modbus module, such as Promux PM6RTD

In a nutshell, keep the factory settings on the PM6RTD : 9600 bauds, 1 stop bit, no parity.

PM6RTD RS485 terminal block 4 3 2 1
connector 4- 3+ 12V+ GND

Adjust the modbus address with the switches on the front

modbus address S1 S2 S3
1 ON OFF OFF
2 OFF ON OFF
3 ON ON OFF

RTU mode

Use a USB to serial adapter, eg the moxa uport 1150 - download MOXA uport drivers for linux/windows.

If using a window desktop, go to the device manager and fit the Moxa so it works in RS485(2W). Here the Moxa appears to be on COM1

moxa uport conf

promux 4- 3+
cable white green
uport 1150 R-(D-)=4 R+(D+)=3

TCP mode

modbus TCP wiring

smartflex RS485 terminal block 1 2 3
connector GND TxRx+ TxRx-
promux 4- 3+
cable white green
smartflex 2 3

basic testing and discover how to configure

Once the promux module powered and connected via RTU or TCP, make a simple test with modbus doctor. Even without any sensor, you can check the serial on register 0. It should be something like 96D (upper byte = software version, here 9, lower byte always = 109 ie 6D)

The PM6RTD supports various RTD types :

number RTD Type
1 PT100
2 Ni120
3 PT1000
4 Ni1000 DIN
5 Ni1000 Landys&Gyr
6 Ohms 10 - 400 ohms
7 Ohms 100-4000ohms
register number description
99 modbus address or unitId
100 RTD Type
101 Line Frequency (50/60)
102 Units Type (1=°C, 2=°F)

Please note register 99 is read only

Here is a screen capture for a PM6RTD configured with modbus address 2, PT100 and °C

PT100 conf 1

if DIP 10 is OFF, communication settings are 9600 bauds, no parity, 1 stop bit

if DIP 10 is ON, communication settings can be programmed :

register number description
120 Baud Rate (2400, 4800, 9600, 19200, 38400,57600,115200)
121 Parity (0 = none, 1 = even, 2 = odd)
122 Stop Bits (1 = 1 stop bit, 2 = 2 stop bits)
123 Reply Delay (0 = Disable, >0 = Enable)

PT100 conf 2

PT100 wiring

wiring the PT100

with the PM6RTD, sensors values can be found from register 1 to 6

thermocouple wiring

Composition : copper / Constantan (copper + nickel)

From −185 °C to 300 °C ;

accuracy +/-0,1 °C from −200 °C to 200 °C.

CEI 584-3

  • brown rubber sheath
  • brown = +
  • white = -

Use the PM8TC isolated module

with the PM8TC, sensors values can be found from register 1 to 8

using a TCP datalogger

in case of a demonstrator instrumentation, with a lot of data to record, the HIOKI 8402-20 is a good choice

Using the HIOKI 8402-20 datalogger with a universal analog input unit LR8501

Hioki web site

HIOKI_full_view

HIOKI_TC connexion

Configure the HIOKI 8204 for DHCP and connect it to the smartflex via an ethernet cable

Define a static DHCP lease for the HIOKI, using its MAC address :

smartflex LAN conf

use the specific Hioki socket interfacer for emonhub :

[[HiokiTCP]]  
    Type = EmonHiokiTcpInterfacer
    [[[init_settings]]]
	    IP = 192.168.2.3
	    port = 8802
    [[[runtimesettings]]]
           pubchannels = ToEmonCMS,
           nodeId = 1
           # in seconds
           interval = 10

node configuration

[[1]]
    nodename = Hioki8402
    [[[rx]]]
       names = TC1,TC2,TC3
       channels = 1,1,1
       voice = 1,2,3

There is no datacode to fix : the HIOKI is streaming ASCII and the decoding is integrated to the interfacer

to understand how to interrogate the HIOKI opening a TCP socket : python building block