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Modbus holding register refresh rate

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We have one issue.

Could you please advise me?

 

<Issue>

PDMM set to holding register of Modbus, then external-controller is read old data. (Read holding register)

Add to wait-time (about 500ms) before external-controller is read, can read new data.

 

<Question>

Can I change Modbus refresh rate setting?

 

<Note>

We use “MODBUS Slave” for motor control.

External-controller communicate to PDMM by Ethernet.

For example, External unit set start-trigger to holding register, then PDMM start controlling motor.

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The Modbus update rate on all of the AKD products is limited to about 20ms.  So you should be able to increase the update rate, but don't set it faster than 20ms.  I recommend 50ms or 100ms just to have some head room, so the communication buffer doesn't fill up.

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Thank you for your answer.

I try to set wait-time to 100ms in external-controller. But, this issue is not clear. I think refresh rate of external-controller must be changed, also. But, it is maybe difficult...

Isao Eguchi - Thu, 09/03/2015 - 19:23
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As stated 200 msec is the fastest Modbus TCP/IP update rate published for the AKD-PDMM. If you need 30 msec communication update rate, we recommend going to another, faster  network that  the product supports:UDP, HTTP, ProfiNet, or Ethernet/IP.

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Thank you for your answer.
I will consider it...
But, the impact of application is large.

Isao Eguchi - Sun, 09/06/2015 - 17:28
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Please see the following section in the KAS IDE help:  Introducing Kollmorgen Automation Suite > KAS Breakdown > Human Machine Interface. Included is the following:

“This communication is done in the background, asynchronously, every 200 milliseconds. Variables defined in the HMI (see Map Variables to HMI) to describe the interface are passed to the PAC or PDMM/PCMM this way. This means there is no data coherency in the data exchange because the variables read by the Modbus do not come from the same PLC cycle. As this data has a rather low priority and is interpreted by human feedback, it should never be noticed by the user.”

The Modbus Refresh rate cannot be changed in the PDMM. The best possible update rate is dependent on the amount of data across the ModBus TCP/IP. Note:The AKD-PDMM has different Modbus TCP/IP capabilities than the other AKD versions due to the PDMM control card in the AKD-PDMM.


What data update rate do you need with the PDMM? How much of a time delay is acceptable?

 

 

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Thank you for your answer.

I need to improve throughput time.

Of course, it is perfect that the delay-time is zero. But, I understand this is impossible. So, it is acceptable that the delay-time is shorter than 30ms.

Isao Eguchi - Thu, 09/03/2015 - 19:19
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