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Power monitoring Module


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Have developers/integrators at Unitronics ever thought of intoducing Power monitoring modules? Then Unitronics OPLC's will make perfect and cost effective Power meters / analysers / data loggers - a very 'hot' product at this time with ever rising energy costs.

All needed for such a module is:

1.Three 0-5A analog inputs to accommodate the current CT's

2.Three 0-600V ac/dc inputs

3.One Neutral input, and

4.A temperature probe (eg PT100) input.

5. A software FB to calculate/measure the frequency from a voltage input

Looking forward to Unitronics' response.


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It's not so simple, as described in initial post. To be able to measure power, you need to follow both voltage and curent waves. They are 50/60 Hz. This means you need much faster analog inputs.

If such module will be developped, do you think it will be sensitivelly lower in price than existing power meters the market is full of?

When you say that you see potential, are you really ready to sell/use at least 200-300 such modules per year? What is the price which can make such module attractive?

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Dear All,

Thank you for answering / commenting on my suggestion.

I agree with my friend Emil about the cost of such a dedicated / specialized module, but this module as described by Emil would be suitable for power analysis, including harmonic content, THD, min. max. voltage and current values, etc. Perhaps it is my mistake to have written power analyser in my original post - a module with the described inputs but with 'normal' analogue inputs would be suitable for power metering, alarming, instant (average) values, etc - I believe, without being an expert, that this would not be so expensive. Imagine all the benefits an OPLC (especially the enhanced family) could support for such a meter!!

Anyhow, it was just a suggestion - no hard feelings if not implemented!!

Best regards to all.


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Hi Emil,

As I think you know, I have shown interest in this topic before (outside the forums).

At this point I have done about 400 hours of work on doing this. You are looking at this issue from the wrong mindset. We do not need an integrated package incorporating a standard power meter that is sellable and mich more controllable. What you are missing in the discussion is that as controller designers we are not looking to make these calculations just for informational purposes but take useful action on the results. Also, the meter function is generally just one small part of an overall control system.

The reason there is a sales potential is that the meters that are out there range from $199 - $799 with differing capabilities, but in all of these cases you are limited to a very meager number of actual IO to control something with. The most I have seen is 4 DI, 4DO, and 2 AO. Then even when the IO is actually there you still need the ability to take the correct action with timers and events that the power meters generally do not make avaialble to you in a way that you can program the way you need to do something useful with the data. I have investigated having my own modules made and it is possible, but for me as a single user the development costs are too high.

The working answer (but not the most cost effective) is to take an existing power meter product with modbus capability and just read it into the PLC and take your actions. This is what we currently do, but for trade reasons Im sorry I can not give details on what those power products are.


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  • 2 weeks later...


I have read the above discussion about advantages / disadvantages of having the own electrical grid analysing instrument. I have such example: Our company buys annually about 20 pcs of Electric grid analysers Circutor CVM 96. Yes, they have reasonable price and they have the Modbus capability. Everything is easy when you need just to read and store data from them. But if you need to generate any software electrical protection, the Modbus commmunication is too slow. For Over/Under frequency protection, Voltage/Vector protection, asymmetry analysis etc., we have to buy very expensive Woodward analysers with electrical protections embedded. But this solution has still some restrictions: There is very difficult to set boundaries for protections just from Vision display, there is nearly no possibility to bypass some protection under special conditions etc. etc. The idea to have proprietary grid analysing module as an special function module is very excitating for me. Try to imagine the possibilities...

I know, it is not a priority for today... but in the future? I would like to have this.

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  • MVP 2014

I was thinking, could Unitronics form a partnership with an existing producer of power analysers? I think there are even several such companies in Israel.

In this case, Unitronics could purchase or license the design for the meter circuit, and add the expansion I/O interface on the front-end. Then put in in a Unitronics expansion module housing.

This is still not a trivial task, but much less costly than developing from scratch.

If such a module could be built into the Jazz as an I/O board, then it's not hard to see where 200-300 per year could be used. I suppose end-user pricing around the $500 mark would be on target.

How many power meters allow you to plug in a modem and support user-configurable SMS? With a Jazz solution we have local control, I/O and also communictions options to allow central data collection or SMS alarming.

When I say I can see the potential it is because this is an area that no-one has cared about in the past, but with the introduction of carbon trading and concerns over energy usage, industrial and commercial customers now want to know much more detail about where their energy is being used. It's not good enough to have just one power meter at the front gate, they want to put them in different parts of the plant. The Australian Govenrment pays special subsidies for businesses who reduce their energy usage. They can only claim these if they prove the energy reductions, which they can only do if they install local metering. I presume other governments do the same, or will be doing this in future.

Whether or not one believes in carbon trading as a solution, energy efficiency and concerns over declining resources are still going to drive demand for this type of product.

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  • 2 months later...
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We have several projects with Circutor, Carlo-Gavazzi and Entes simple powermeter with modbus serial port. The most of them because their datalogger are expensive. With OPLC the possibility of add digital and analogs inputs improve the application.

I think if Unitronics will have a low-costg powermeter like an option we increase the sales about 100-200 units/year. It depends of the final price and the software we can develope. Circutor and Carlo-Gavazzi sell a lot of powermeters because their software of analysis.

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