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Author Topic: Limit switches on modbus/TCPIP  (Read 3801 times)

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Limit switches on modbus/TCPIP
« on: July 16, 2009, 11:33:37 AM »
I had an Adam-6061 sitting unused so I decided to try and get Mach3 to find it and read the some of the inputs.
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The ADAM-6051 provides 12 digital inputs, 2 digital outputs, and 2 counters with 2000VRMS isolation protection.
This mixed-function module built-in Ethernet port and web page.
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I have been able to get Mach3 to see and read the Digital inputs through the testing screen under modbus config but I'm lost at how to tell Mach3 that the home and limit switches are on modbus. I'm also looking at a way to use the 2 counters on my router, there must be something a counter will be useful for :)
I hope to use one of the Digital Outputs to control my spindle on/off function.

Thanks

Offline Jeff_Birt

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Re: Limit switches on modbus/TCPIP
« Reply #1 on: July 16, 2009, 12:04:31 PM »
You can't use any form of modbus for hi speed I/O like homes/limits. The latency between the switch actuation and Mach seeing it will be too great causing all sorts of variance in the sensed position. Modbus I/O is good for thin.gs like user interface switches and lights, or a program running on a PLC that Mach only needs to know the status of
Happy machining , Jeff Birt
 
Re: Limit switches on modbus/TCPIP
« Reply #2 on: July 16, 2009, 12:24:46 PM »
You can't use any form of modbus for hi speed I/O like homes/limits. The latency between the switch actuation and Mach seeing it will be too great causing all sorts of variance in the sensed position. Modbus I/O is good for thin.gs like user interface switches and lights, or a program running on a PLC that Mach only needs to know the status of


Yes Jeff is correct. When reading Modbus at 25ms (40Hz) you can have a varing delay of up to 40mS, so it is no good for home switches.

You can use Modbus for limit switch depending on the dynamics of your machine and how far it moves in 25ms. That said a more responsive input such as through the parallel port or Smooth Stepper is desirable.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: Limit switches on modbus/TCPIP
« Reply #3 on: July 16, 2009, 12:30:30 PM »
Well that is a downer. I did notice there was some latency when reading the switches. I have been able to get the second parallel port working with Mach3 so the Adam-6051 is more of a toy anyway.
That leads me to another question, why 25ms?
Re: Limit switches on modbus/TCPIP
« Reply #4 on: July 16, 2009, 05:57:28 PM »
Well that is a downer. I did notice there was some latency when reading the switches. I have been able to get the second parallel port working with Mach3 so the Adam-6051 is more of a toy anyway.
That leads me to another question, why 25ms?

25mS is the resolution that you can ask Mach3 to poll the modbus devices, so worst case is that the limit switch closes just after Mach3 has polled the device and the limt switch closure won't be detected until the next read.

Cheers,


Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com