PLC recommendations

Just read this:
cjd1969 said:
We find it very hard to get Siemens to come to site and help without paying them.
Unless there is a major failure in the equipment they have supplied, Siemens will not give free onsite support. I find it naive to expect that.
Other vendors that are eager to capture you as a customer may be willing to give you a free one-time onsite visit, if they believe it will clinch the deal. But they wont continue to do so. And I think one visit should not make the difference to decide something so significant as a change of platform.

To me the whole thing about the PID loops sounds as the real problem is that you are short for time. Switching platforms wont buy you more time.
 
It looks pretty good but not for S7-300 i believe.

The IM-151 suggested by Jesper would meet the cost saving (partly) and would allow me to reuse my code which is all good but i am interested in ideas etc... I see IDEC has dedicated PID modules that seem to mimic a proper temperature controller for example

Cheers

That is for s7-300. When you look at left,you see im151-8 configured. There is separate PID for temperature and for other processes.

Have not used it, but it is there and could be best, most cost avare way for you.
 
I can give you another option which I use.
Use IM-151-8 and Red Lion G3 with CSPID2.The PID loop is outside the PLC and not effected on the PLC performance.It Connected by Ethernet and very easy to set up including auto tuning.It save the analog card and the extra price is the controller.
 
Just read this:
Unless there is a major failure in the equipment they have supplied, Siemens will not give free onsite support. I find it naive to expect that.
Other vendors that are eager to capture you as a customer may be willing to give you a free one-time onsite visit, if they believe it will clinch the deal. But they wont continue to do so. And I think one visit should not make the difference to decide something so significant as a change of platform.

To me the whole thing about the PID loops sounds as the real problem is that you are short for time. Switching platforms wont buy you more time.

I agree. However in the past I have had site visits labelled as training or sales visits.this was plc manufacturers/ drive manufaturers / etc. In these hard times everyone is cutting back on any expense. The project was already over spent so I was unable to raise a PO.

It is correct i had little time for PID tuning for the cooling loops.
I had some reasonable terms but the next day these did not work.

Basically I had a modulating valve controlling cooling water into a heat exchanger. The product needed to be cooled (85 to 65 or 85 to 30) depending on the customer selection switch.

I found the PID would work OK and the PID would close the valve about 1 degree above the setpoint but the HX itself was still cold so the cooling continued for about 10 more degrees until the hot product warmed it up. Once the product PV was just above the SP the valve was opening under PID over around 8 seconds to achieve fully open. Because the HX needed to cool itself AND the product the initial few seconds did nothing to the product temperature. This reaction time meant that the product was about 12C above SP before the cooling restarted enough to reduce the product PV.

So the swing was about +12 and -8 of the SP

I ended up using clamps to severly restrict the pid and looking back i should have written my own code to replace the pid. The normal pump speed and temperature controller pids work fine and were tuned easily. I do understand the basic concepts but not the seeper maths

I have also considered using seperate temperature controllers as suggested by people here (like old school stuff we did years ago) but this is also more expensive due to needing variable setpoints and PV temperatures onto the HMI which needs comms or analog io to achieve.

The IM-151 and the cheaper HMI would be a good solution but i am still open to other cheap(er) ideas

Cheers
 
As you have already seen the VIPA and you know detailed Step7 Programming.
the Vipa will be the cheaper better option.
Unless you are use to programming the other PLC's.
I assume you use Process Meters to set/test your PID loops.
One other PLC range is Beckhof - that may be too expensive though.
 

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