Solve Communication issues between HMI and PLC of Schneider Make
21 June, 2020.
In this post, we will cover the basic topics on how to
troubleshoot problems faced by programmers in establishing communication
between a PLC and HMI of Schneider-Make.
Hello programmers. Here we will discuss the common mistakes made by
programmers in establishing proper communication between a PLC and HMI of
Schneider-Make. We will discuss here the two widely used protocols; Modbus RTU
and Modbus TCPIP. The HMI software we will cover is Vijeo Designer and the PLC
softwares that we will cover are Ecostruxure Machine Expert-Basic, Somachine
V4.3 and Unity Pro/Ecostruxure Control Expert.
Before moving ahead, refer the
below image. When communication is not happening, then it will show as yellow
triangle besides the display and popup the message below. We will divide
our lesson into three topics. The topics here means, the three types of issues
and it’s solutions. So, without
wasting any time, we will jump to our study and review each and every cases
normally faced. ·
The basic and foremost thing to check is this topic. We go
to all the advanced steps and then we realize that it was this basic thing
which we forgot to check. Always check the type of cable which you are using
for communication.
Basic Steps involved in checking communication between PLC and HMI:
Proper cable configuration and
cabling:
· Now, let’s look at the cable configuration used for Modbus
TCPIP and Modbus RTU (RS-485 hardware). Refer the below image for
understanding. The first image with three wiring types show the practice used
for Modbus RTU configuration. The second image with two wiring types show the
practice used for Modbus TCPIP configuration. If there are multiple PLC’s and a
single HMI, then refer my topic (Troubleshooting
Modbus code Schneider PLC - Part_1_General Practices in Modbus) for proper
cabling practices; if the protocol used is Modbus RTU. Modbus TCPIP is simple
and just requires a series of Ethernet connections on a hub switch with
distinguished IP address.
Proper configuration in software:
·
The next step is to check the communication settings done
in software. Ensure that the settings in PLC and HMI are proper; otherwise
communication won’t happen.
· Refer the below image. It shows the settings available for
Modbus RTU. The settings shown are default one; which appear when you select
this protocol. Ensure that the transmission speed, parity bit, stop bit and
slave equipment address is correct or not. Also verify whether you have
connected the cable in COM1 or COM2.
When
there are multiple slave devices connected, then the settings will be as below.
Only equipment address will differ. Make sure they don’t clash with each other.
The below
image shows the settings for Modbus TCPIP. Make sure the IP address of target (HMI)
and the slave device are not similar. Also ensure that the Unit ID of slave
device is proper. Multiple slave devices will show same settings as referred
above. IP addresses and Unit ID will differentiate between them.
· Now, let’s move ahead to PLC configuration. Refer the below
image. It shows the settings available for Modbus RTU in Machine Expert - Basic.
Ensure that the baud rate, parity bit, stop bit and address are correct and
match with that in HMI. Also verify whether you have connected the cable in SL1
or SL2.
The below
image shows the settings for Modbus TCPIP. Make sure the IP address of PLC is
similar with the equipment configuration in HMI.
·
Now, let’s move ahead to
Somachine V4.3. Refer the below image. It shows the settings available for
Modbus TCPIP. Ensure that the IP address matches with that in HMI.
The below
image shows the settings for Modbus RTU. Ensure that the baud rate, parity bit,
data bit, stop bit and address are correct and match with that in HMI. Also
verify whether you have connected the cable in SL1 or SL2.
·
Now, let’s move ahead to Unity
Pro / Ecostruxure Control Expert. Refer the below image. It shows the settings
available for Modbus RTU. Ensure that the settings match with that in HMI.
The below image shows the settings for Modbus TCPIP. Ensure
that it matches with that of HMI.
Also
ensure the settings in below image; which most people forget to see.
Proper addressing of variables:
After understanding the above two methods, let’s move to
third method. It deals with proper addressing of variables. We either enter
improper address (in HMI, it will be %MW100 and in PLC, it will be %MW101) or
keep the wrong format of variable (in HMI, it will be INT and in PLC, it will
be REAL). Machine Expert – Basic software has one-to-one addressing and you can
easily troubleshoot variable properties. But, in Somachine V4.3 software, the
addressing is same for integer values; but different for double-integer and
real values. For example, if the PLC address is %MD50 in real format, the HMI
address should be %MF100 (the double of PLC address). The addressing is also
same in Unity Pro software. Refer the below image for an example of these three
softwares. It shows various variable properties in HMI. Ensure that you have
selected the correct Modbus Equipment
in variable properties.
Refer the below image; which you have seen earlier too in the
topic. Unticking IEC61131 syntax will
allow you to enter the variables in old Modicon format (40001 instead of %MW0).
Keep double word order option as low
word first.
I have covered
the general principles which normally are followed to troubleshoot communication
issue. I have also not attempted to cover every type of device.
Each manufacturer has unique ways of handling problems, and there are many
other sorts of solutions that I have not included here.
Thank you guys; I hope you enjoyed reading the practices normally used
for this type of troubleshooting in industrial automation.
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