120vac as an Input

Hey Everybody
I am knew to the PLC world. I am trying to design logic for a project that requires 120vac as an analog input. I need to get this to the level that the PLC can work with. I have looked into RMS A/D converters and rectifying this 120vac. Does anybody have this type of knowledge? This input will be for monitoring and comparing. I actually need 4 inputs of this type.


Lionel

120 VAC analog?

Highly improbable. If you identify the sensor, the task, and the logic we can probably help.

120vac input

I'm back

I plan on monioting these 120vac inputs. If the 120vac is missing. I want to start a generator. Once the 120vac is back. Turn off the generator. I also want to show the AC voltages on a operator interface for moniotring. There will be 1 inputs from shorepower,1 from the generator and 2 from a panel box. All of these inputs are very low current because of the monitoring only idea.

Hope this helps
Lionel

Action Instruments is another possible source (as well as many others).

Action has 2 units that will give a voltage or current output in proportion to an AC voltage in the range you're looking for.

Look at the AP6830 or Q466.

Unless you REALLY want the voltages displayed on the operator interface, you can probably save a few bucks by simply monitoring for "AC present" with a digital input, and display the voltages on a simple panel meter with a selector switch (or multiple meters).

beerchug

-Eric

Hey Ken, where'd your post go????

Oh, I get it. You want an AC Voltage Transducer, to proportionally convert the voltage on your powerline into a more common PLC analog input format, such as 4-20 mA current loop. Google should find dozens.

I'm surprised something like this isn't offered by the generator maker. Or are you integrating the generator control into a general purpose shipboard control system ?

I know that big backup generator sets have sophisticated synchronizing equipment on them to be sure they're set up to duplicate the phases coming from the power grid... I hope somebody experienced will chime in on how this can be done with a simple 120V single-phase generator, or if you'll just need to disconnect the generator, wait, then reconnect shore power. It's something I've never had to work with before.

Hmmmm, changed your mind, eh?...

beerchug

-Eric

120vac

Hey

All of this design is for a motorhome with a diesel Generator. This plc will monitor ac,dc,ac-current and temperture. The biggest problem is getting the ac to the level of the plc.

Lionel

Re: 120vac

Lionel said:

The biggest problem is getting the ac to the level of the plc

Click to expand...

Well then, a signal conditioner is what you'll need.

Happy motor(home)ing!...

beerchug

-Eric

Actually any RV parts store will sell items that do this that may be cheaper than trying to incorporate a plc to do it. I assume this is an Onan genset since you mentioned a Motorhome..ususally 5kw to 10kw range. The device is called a transfer switch.

There are many approaches to this. The voltage you can send to the plc as a digital input to show power is good, you can also use a meter to display the voltage. In this case you would use 2 inputs to determine if city/utility power is missing and start genset then switch contactor to provide generator power, the second input is to sense the genset voltage. Allow time from loss of power after genset starts before doing the switch. You will need 2 contactors rated for your Motorhome, most small units are in the 30 amp range but its not unusual for larger units to have 60 amp 240v (2-120v with neutral).

The biggest problem here is the plc..what will power it when utility power is gone? Its possible to use a UPS that will allow time for the genset to start and switch or were you thinking of using the 12v system thats on most Motorhomes?

This can be done a lot simpler and cheaper without the use of a plc but the ac I would just monitor as a digital input to show power is good but you could also convert it to 1-10 volt analog input and do some scaling to match the ac input. The DC will be simple. AC current will require the use of current transformers (CT) which can be obtained to match an analog input then scaled, temp usually can be sent directly to an analog input then scaled...then all the above displayed on an HMI if that is what you want to do. Its simpler to just use analog meters for the voltages with auto switching to transfer to whatever power source is being used.

Lot of options in this scenario, state what plc and if using an HMI then the advice can be more specific.

120vac

Hey again

I really want to do everything in one package with the PLC.

Reasosn: One package- when selling the MH you can take everything with you. A screen is more impressive than meters/gauges. There is already something on the market that will start the gen. There is nothing as a total package of monitoring and gen start. With a plc, it is a never ending project. If the customer desides that they want an alarm or to monitor anything else. It can be done here,just send them a chip and give instructions for the inputs/outputs.

Lionel

There is already something on the market that will start the gen. There is nothing as a total package of monitoring and gen start.

Click to expand...

I have to disagree with this, the newer model MH's have solid state/microprocessor based systems with either digital, graphical or PC displays offered as options. As I stated Onan, Generac and others package systems that perform all these functions in a variety of ways.

As a reference:
http://www.cutler-hammer.eaton.com/unsecure/cms1/TD01602003E.PDF

Another option is to look at using digital meter displays that can display the options you want AND send the info to the PLC via RS232 etc.
http://www.predig.com/Products/PD695.html

http://www.predig.com/Products/PD765.htm
In other words let the display measure the values and use the plc to control the process.

The means to do this is open to your imagination, just think of it then look/search for the devices to do what you need to do.

NOTE: Never think that a plc HAS to actually be fed values directly to its inputs, other devices can be used that may communicate to a plc.

I cant state any specifics on what options to use with your PLC...because you havent stated what PLC you are using. Its possible that you may need another form of microcontroller based system like Unitronics.
http://www.unitronics.com/products.htm

Another option is to use signal conditioners as was stated.
http://www.apcs.net.au/webdraw/ds70111/ds701115.pdf

Let us know what you come up with.

120vac

The plc that I am considering is the circuit board style. I want this because of size and it will not look like an industrial type. I have found a company in Gasport,NY that may have what I need. The company is Entertron. This company is investagating my options to support the 120vac. I know there is probably something in the field simular
to my needs. I would like to develope my own and have open options to growth.

Lionel

(Quote
Originally posted by Lionel
The biggest problem is getting the ac to the level of the plc

Actually I see that as being the easiest, It doesn't matter what PLC you are using you are going to have some sort of digital AC or DC input module. If you have 120vac module just monitor the 120vac, if you have a 24vac module just use a 120vac/24vac transformer and monitor the output, if you have a 12vdc module use a 120/12vac transformer and a full wave bridge rect. You don't need an analog signal if you just want to detect the presents of 120vac. But if you desire an analog signal then use a transformer to reduce the 120vac to either 10vac or 5vac and use an analog module configured for voltage. Zero to 10v, or zero to 5v will be proportional to the zero to 120vac. Rectify if dc is needed.


Roger

Lionel we are familiar with Entertron, their rep (Stephen Luft) is a regular here. From what I have seen I would say that they will problably provide the options you need to do what you are attempting.

OR provide the options needed for this endeavor.

Good Luck.

Thanks everybody

The project would be simple if I just wanted to see the presents of the 120vac. Since I want to see the values of 4 different 120 circuits. This is what is difficult.
Many have mentioned that there are devises on the market already but, not like what I want. I could probably use gauges/meters. This would make this package too big for the spaces provided in a motorhome.

The circuits that I have checked into use a AD536a RMS A/D converter. We are going to try and go this way if all else fails.

Lionel