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Niagara Jace with Modbus TCP

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Discussion starter · #1 ·
Hello everyone,
i have a modbus TCP network with field controllers (about 60) under a Distech EC-Bos8. Everything is working ok except of the speed of my network. COV is coming with a lot of delay to my station, sometimes this delay is close to a minute. Network seems ok, some bacnet devices i have (about 2000points) are sending-receiving almost constantly.
Is there a way to make my Modbus TCP network faster? I tried changing polling and ping time with no significant results.
Thanks
 
#2 ·
The Modbus protocol does not support COV. Are the COV's you're talking about from the BACnet devices? If you're using COV's on BACnet, then they shouldn't be sending-receiving almost constantly. The BACnet devices should send COV notifications only when values change.

I assume you're using the JACE to talk to both Modbus/TCP and BACnet/IP devices at the same time. The only way to read Modbus values from a device is to poll, so decreasing the polling time should improve performance, unless your JACE is already going as fast as it can (which sounds to be the case). This could be a bandwidth-type of issue. The JACE may be spending too much time sending/receiving packets to/from the BACnet devices to be able to poll the Modbus devices quickly.

A Wireshark capture would tell you exactly what the JACE is doing and what's happening between the Modbus requests. This could also show other issues that may be causing the delay.

I'm sure someone else here that's more knowledgeable on the JACE's configuration and tuning settings can provide further recommendations on settings to check in the JACE itself.
 
Discussion starter · #3 ·
jschulze said:
The Modbus protocol does not support COV. Are the COV's you're talking about from the BACnet devices? If you're using COV's on BACnet, then they shouldn't be sending-receiving almost constantly. The BACnet devices should send COV notifications only when values change.

I assume you're using the JACE to talk to both Modbus/TCP and BACnet/IP devices at the same time. The only way to read Modbus values from a device is to poll, so decreasing the polling time should improve performance, unless your JACE is already going as fast as it can (which sounds to be the case). This could be a bandwidth-type of issue. The JACE may be spending too much time sending/receiving packets to/from the BACnet devices to be able to poll the Modbus devices quickly.

A Wireshark capture would tell you exactly what the JACE is doing and what's happening between the Modbus requests. This could also show other issues that may be causing the delay.

I'm sure someone else here that's more knowledgeable on the JACE's configuration and tuning settings can provide further recommendations on settings to check in the JACE itself.
Click to expand...
Hi jschulte,
Yes, i am using my ip port for both BACnet and Modbus TCP. With Change of Value i meant that when changing a Digital Input from 0 to 1 in my controller the change 'arrives' sometimes after a minute in my Jace. This is not happening in BACnet.
Thanks
 
#4 ·
If your poll times are faster than a minute and you aren't seeing changes that fast I'm thinking you are backed up in what that modbus driver can poll. You may need some points to refresh much slower to enable some select important points to refresh faster.
 
Discussion starter · #5 ·
MaxBurn said:
If your poll times are faster than a minute and you aren't seeing changes that fast I'm thinking you are backed up in what that modbus driver can poll. You may need some points to refresh much slower to enable some select important points to refresh faster.
Click to expand...
I changed the polling to my Digital Inputs from Normal to Fast and things got better. I will check the next days if something else is damaged from this change (offlines, fault status points or so...)!
 
#6 ·
Sounds like your Modbus devices may not be setup properly or the devices are serial devices connected to a serial to IP device like a Moxa MB3170.
A few things to check:

If your IP device is actually a gateway to to multiple serial device address, make sure to use the ModbusTCP Gateway Network and devices (This is actually a separate network that doesn't need to be under the ModbusTCP Network) Tridium allows you to create multiple ModbusTCP devices using the same IP address but depending how many devices you have, performance can be slow as you described.

Under the ModbusTCP property sheet open the poll scheduler and look at average poll speed and busy time. If its been running a while reset the statistics to see the network performance is. IP speed for most true IP devices (not serial gateways) should be around 10 ms. Also look at the busy time my guess is setting that to default of fast (5 seconds) your busy time is going to be really high.

Last thing to check on each device is to setup the Device Poll Config which will poll a range of contiguous registers with one request (like Bacnet ReadProperty Multiple)
 
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