Siemens S7 = How to acquire voltage and current?

[ElectroSeb]

Hello,

(Sorry fot my english)

I'm using a S7-300 with CPU 315-2DP for my future house.

I need idea to how to acquire voltage and current in my PLC ?
Wich card i need and wich devices ? 4-20mA, other ?

I want to acquire these values and multiply them to know my consumption in W.
To later, one more time multiply this value with ...€ / Kw/h.
Then statistics and a table of values by day, week, month, and year.

How to acquire current and voltage in my PLC ?
Thanks for your help !

ElectroSeb

 

[Lancie1]

ElectroSeb,

The most practical card to use in a PLC to input currents would be the 4 to 20 ma Analog Input card. For voltages, the 0 to 10 volts Analog Input card may be used. In addition, you also will need some separate current transducers to change your house currents from 20 Amperes to 20 miliAmperes. You may need a few other ranges for larger applicances. That will take care of the currents. However, you will need many 4-20mA Analog Input cards to be able to measure all appliances at the same time. I suggest that you measure them one at a time, over a short cycle time, using only one 4-20 mA input. You would still need seperate transducers for each input. Use digital relay outputs to switch your current input wires to the one 4-20 mA analog input. This method will reduce your cost for analog cards, and still measure all devices. This is called multiplexing, and is a way to measure many inputs over a short time period, using only a small number of analog inputs.

For voltages, you will first need a transformer, to step the voltage down to approximately 15 volts alternating current. Then connect this lower voltage to a solid-state electronic rectifer to convert the signal to direct current. You want to end up with 10 volts DC maximum. Your house voltages should vary very little. I suggest that you use only one voltage input for the entire house, and use this one voltage value to calculate the power used by all appliances. You will still have enough accuracy to calculate your total Watts.

 

[leitmotif]

I would think a data logger would be more appropriate for this application. You can get them with the voltage and current sensors (outside temp sensor, wind velocity, etc etc) and with computer interface to do your calcs.
If you want PLC to control the house then let the PLC do the recording also -- most cost effective.

 

[ElectroSeb]

Hello Lancie1,

Thank you for answer.
So, i think for voltage i can keep always value 230 and don't use device to measure. I also think that value does not vary so much.
For the moment i want to acquire only general consumption, so only one current transducer just after main breaker.
For current transducers, do you have an example, website, company ?
And for analog input card, wich one ? Because i can find 8bits, 12 bits... How to choose ?

Thank you very much

Electroseb

 

[seppoalanen]

Current transducer: MCR-S-10-50-???? Phönix (55A)
A-Input unit: 6ES7 331-7KF01-0AB0 Siemens 9/12/12/14 bits, see the manuals.

br. Seppo

 

[Tom Jenkins]

You can either use voltage and current transmitters to get 4-20 mA, or use a kW transducer instead which will be more accurate.

You may have another option. Here in the US the electric company, for a small fee, will install a pulse relay on their existing meter. This gives a dry contact closure every so many kWh. It is usually a slow (every few seconds) 50% square wave. You can take this into a discrete input and use a counter. Then your readings will agree with the power company's exactly.

 

[ElectroSeb]

Hello everybody,

I prefer use current transmitter, so i can use this value for something other idea.
Tom Jenkins, do you have a sample of Kw transducer ? I never see one, i don't know it exist.
Seppo, for your Phoenix current transducer, do i need to use a "Tore" ? By example this (http://www.kwk-messwandler.de/en/produkte.php)?
Or it is possible to directly find a tore with input from 0 to 50A and output 4-20mA ?

Thank you

ElectroSeb

 

[Tom Jenkins]

Here's one: http://www.loadcontrols.com/products/products.html

 

[Jimmie_Ohio]

Power Savings via Display

During a recent visit to a "home automation" forum, I saw a post about someone who set up a display to show the current that was being used in the house. This was on a constant display in a prominent place (next to the refrigerator, perhaps?)

The fellow who posted this said his kids made a game out of seeing how low they could go by keeping unneeded lights off, etc. According to his report, his electric bill went down considerably during this process.

Bottom line: If you are interested in monitoring power in your home, consider adding a display or recording capabilities so you can "see" what you are using.

 

[ElectroSeb]

Hello Jimmie,

i don't want use a display, my problem is just to acquire current, after, i use WinCC Flexible to make curves, table and value history.
WinCC Flexible will be my main control for my house.
Me too that's a little for game, if i see big curve or anormal table, i can think wich device can be not used to economize ?
I want to adjust temp, when i'm absent, the night and during the holidays. So i can check if Kw really down or if i need less temp.
Yes after i have to find just middle between good temp for everybody, and good temp to economize.
So, for current transducer, i think to use a "Tore", i can find this in a big inverter. I search this next week if i have time.

Thank you.

 

[ElectroSeb]

Hello,

i have find 6 "Tore" from a KEB COmbivert inverter,
Company: Yaskawa - Reference: UND-300B/..
But i can't find documentation about this to know if that's a 0-10v or 4-20mA, or... ???
There is connector, inverter side: 5 wires: 1 shield, 1 black, 1 green, 1 white, 1 red. Side of "Tore": 4 wires: 1 black, 1 green, 1 white, 1 red. If there is a shield, i can think to a 4-20mA. Maybe...
I try to find manual of this Tore, or manual of KEB Combivert inverter.
If you have this, can you send me this in french or english to [email protected]

Thank you