PLC/SCADA options?

nigel s · Dec 1, 2007

Hello chaps; I wonder if anybody could point me in the right direction?

I need to specify (& eventually program/commission) a control system for a test chamber which will be used to assess the performance of supermarket style refrigerated display units in accordance with BS EN 441. The control side of the job is simple & comprises just 3 PID loops for temperature, humidity & circulating air velocity. But we also need to monitor & log approximately 30 analog inputs from sensors on the appliance under test over a 24 hour period (I'm not sure at this stage at what kind of time intervals until I get access to the BS document but could be say 5 minutes) & then - after some calculations relating overall energy input to actual refrigerating capacity generate a summary in Excel format.

I think the question would be - is this a basic PLC plus SCADA application or would the number of analog inputs - which are only being logged - require a more complex PLC than could be justified?

Is there maybe a way of using a very minimal PLC for the control of conditions in the chamber, & some other means of data acquisition & processing for the analog inputs?

I envisage that we'll be using a touch screen as an interface to the system. I know some of the HMI's available can have quite a lot of inbuilt intelligence but am uncertain as to whether they could handle the logging & calculation aspect.

Has anybody done anything similar?

surferb · Dec 1, 2007

I'm not familiar with BS EN 441. My recommendation is that you implement the more complex aspect of the logic in the PLC - your hardware requirements will not be steep.

For the rest I'd recommend checking out FactorySQL and FactoryPMI from Inductive Automation. I've done 2 similar projects to what you're describing - one of which used industrial touch screen PCs.

In fairness, have the PLC deal with the complexity and use an SQL database for the monitoring/logging/reporting. This will simplify the SCADA app to a level where most packages should be fine.

Your project really isn't that complicated. The specific industry has little to do with the requirements.

nigel s said:
Hello chaps; I wonder if anybody could point me in the right direction?

I need to specify (& eventually program/commission) a control system for a test chamber which will be used to assess the performance of supermarket style refrigerated display units in accordance with BS EN 441. The control side of the job is simple & comprises just 3 PID loops for temperature, humidity & circulating air velocity. But we also need to monitor & log approximately 30 analog inputs from sensors on the appliance under test over a 24 hour period (I'm not sure at this stage at what kind of time intervals until I get access to the BS document but could be say 5 minutes) & then - after some calculations relating overall energy input to actual refrigerating capacity generate a summary in Excel format.

I think the question would be - is this a basic PLC plus SCADA application or would the number of analog inputs - which are only being logged - require a more complex PLC than could be justified?

Is there maybe a way of using a very minimal PLC for the control of conditions in the chamber, & some other means of data acquisition & processing for the analog inputs?

I envisage that we'll be using a touch screen as an interface to the system. I know some of the HMI's available can have quite a lot of inbuilt intelligence but am uncertain as to whether they could handle the logging & calculation aspect.

Has anybody done anything similar?

burnerman · Dec 2, 2007

This doesn't seem to be an application that needs a plc unless there are some more control functions that you haven't mentioned.

For the 3 PID control loops you could buy stand alone controllers at less than £200 a piece and there are plenty of low cost data aquisition packages on the market which can log data and export the data in csv format which can be imported to Excel.

Could the energy calculations be carried out in Excel or would you need a real time display of these?

JesperMP · Dec 2, 2007

nigel s said:
I think the question would be - is this a basic PLC plus SCADA application or would the number of analog inputs - which are only being logged - require a more complex PLC than could be justified?

40 analog inputs can be handled by all except the very smallest PLCs.

nigel s said:
Is there maybe a way of using a very minimal PLC for the control of conditions in the chamber, & some other means of data acquisition & processing for the analog inputs?

There is no law that says the control and data logging have to be made with the same solution. You could control the proces with a small PLC and then log data with LabView for example.

The question is if the PID control is a part of what should be logged.
If so, then an integrated solution is necessary.
If not, you are more free to do what you like.

The Factory PMI solution sounds nice, but maybe a little bit expensive (5000 USD for everything if I got my math right).
Slightly less expensive is for example a datalogger from software toolbox, that cost 500 USD for logging to CSV files, and a bit more for logging to a database. Add approx 500 USD for an OPC server.
http://www.opcdatalogger.com/
This is just an example, there may be many other solutions, and these will depend on the PLC or dataackuisition hardware you choose.

surferb · Dec 2, 2007

Hard to tell from the post how large a project OP is attempting, how complex his calculations and what kind of budget he's dealing with. More detail would be useful.

Jesper - In response to your comment comparing FactoryPMI to OPCDatalogger (also resold by Software Toolbox). FactorySQL is the equivalent product at $1995 (retail). It will log and do all the calculations mentioned to pretty much any SQL database - NOT .CSV files (by design). It also does more triggered type operations like RSSQL. FactoryPMI is a distributed SCADA app that can run a multisite enterprise. It woulds well for small applications, but the pricing could be outside what OP is looking for - again, need more specific requirements.

There are many cheap industrial "utilities" that may solve your problem as well.

JesperMP said:
40 analog inputs can be handled by all except the very smallest PLCs.
There is no law that says the control and data logging have to be made with the same solution. You could control the proces with a small PLC and then log data with LabView for example.

The question is if the PID control is a part of what should be logged.
If so, then an integrated solution is necessary.
If not, you are more free to do what you like.

The Factory PMI solution sounds nice, but maybe a little bit expensive (5000 USD for everything if I got my math right).
Slightly less expensive is for example a datalogger from software toolbox, that cost 500 USD for logging to CSV files, and a bit more for logging to a database. Add approx 500 USD for an OPC server.
http://www.opcdatalogger.com/
This is just an example, there may be many other solutions, and these will depend on the PLC or dataackuisition hardware you choose.

JesperMP · Dec 2, 2007

Right, I took the price for PMI + OPC server + SQL database to arrive at 5000 USD. My mistake.
For factory SQL + OPC server + SQL server, 2000 + 500 + 1000, it will be approx 3500 USD.

surferb · Dec 2, 2007

Yep, that's about right. Or you could save yourself $1000 with either MySQL Community Server or SQL Server Express Edition for free (MySQL isn't limited like Express Edition).

The full package with FSQL and FPMI comes out a bit higher - cheap for a distributed enterprise system, maybe overkill for a single user terminal (although I have seen it done).

Greatly depends on the scale of OPs project.

JesperMP said:
Right, I took the price for PMI + OPC server + SQL database to arrive at 5000 USD. My mistake.
For factory SQL + OPC server + SQL server, 2000 + 500 + 1000, it will be approx 3500 USD.

nigel s · Dec 2, 2007

PLC/SCADA options

Thanks for all the input. In answer to one of the questions, the PID loops controlling the chamber conditions don't really need to be part of the logged data. I've always liked the idea of using discrete controllers (like West or Eurotherm etc) but it would be good if their parameters could be accessed via a HMI screen - is this do-able?

Regarding the data acquisition part - I'll check the names you've suggested but generally is there hardware available other than the input modules associated with a PLC which will accept the analog inputs? - preferably direct from Pt100 temperature sensors rather than via transmitters.

nigel s · Dec 2, 2007

PLC/SCADA options

Oh yes. I forgot - the calculations; no. these can be done just the once as part of the final report generation process from averages of the relevant collected data.

At least I think so. I'm awaiting delivery of the BS document which I hope spells out how these tests need to be conducted.

surferb · Dec 2, 2007

Not requiring the PID logging does simplify things for you. The parameters should necessarily be accesible via your HMI screen - they're variables, registers, tags, whatever just like any other numeric values that you want to display or input to your system.

I'm not sure where you're going with the hardware question with respect to data acquistion. I'd speculate that would be many hardware options to read your PRTs - you still haven't specified your PLC/controller type. Data acquisition is typically done with a PC based software package that has a "hook" to read values. As Jesper suggested, that's usually OPC.

Could you get more specific on your data acquisition and "calculation" requirements? What about the size/scope of your project?

nigel s said:
Thanks for all the input. In answer to one of the questions, the PID loops controlling the chamber conditions don't really need to be part of the logged data. I've always liked the idea of using discrete controllers (like West or Eurotherm etc) but it would be good if their parameters could be accessed via a HMI screen - is this do-able?

Regarding the data acquisition part - I'll check the names you've suggested but generally is there hardware available other than the input modules associated with a PLC which will accept the analog inputs? - preferably direct from Pt100 temperature sensors rather than via transmitters.

surferb · Dec 2, 2007

Oops, was typing away before I saw the second post. Performing "calculations" on logged data and dynamic report generation is the most viable if you're historical data is coming from an SQL database. In the industrial software world you may find yourself otherwise constrained (read, vendor-locked - paying for their solution as your only option). As Jesper suggested, this can be part of, or separate from, your control portion (integrated or not).

I keep emphasizing the question, "what are your requirements"? On the very simple end, if this is a manually managed process, then using OPC Datalogger to dump your process data to a .csv, then manipulating the data in Excel as the "final report generation process", including calculation, may be sufficient. If you need to store your data for some time and dynamically generate reports that include calculations, then find an SQL database based solution.

I'm not familiar with the term BS. Sounds like I'll be waiting for it...

nigel s said:
Oh yes. I forgot - the calculations; no. these can be done just the once as part of the final report generation process from averages of the relevant collected data.

At least I think so. I'm awaiting delivery of the BS document which I hope spells out how these tests need to be conducted.

PLC/SCADA options?

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