How to interface Analog Panel Meters?

[howie cia]

Hello,

I need to monitor analog panel meters from a generator panel such as voltmeter and current meter (ammeter) that will be interfaced into uP. The voltage range is typically 0-250VAC and the current to be measured is within 5-600A range.

But the problem is I only have an ADC chip that accepts input voltage and current within 0-5V and 0-40mA respectively. These are standard output on most of analog devices.

Anyone who has an idea on how to convert an AC voltage ranging from 0-250V to 0-5VDC? I've tried to use a diode rectifier (bridge-type) followed by a voltage divider circuit to covert AC to DC and downgrade DC voltage into 5V. It work well but I still need alternative solutions. Especially in monitoring current, any idea on how to monitor and interface the current meter readings to uP?

Regards to all,

Howie

 

[MikeMl]

Are the panel meters reading the voltage/current already?

Do you want to "isolate" the uP from the line? (Ground on uP not connected to either side of the AC line)

 

[Space Varmint]

A voltage divider will not give a true reading. I would use an attenuator.

 

[aljamri]

Have you ever considered CT (Current Transformer? they are coming in different ratios, choose the one suits your output. It is been used in almost all the Hi Current measurements and protection.

 

[crutschow]

A voltage divider will not give a true reading. I would use an attenuator.

What's the difference between a voltage divider and an attenuator?

 

[Mikebits]

Did you say 250VAC @ 600 AMPS? Holy cow...

 

[aljamri]

What's the difference between a voltage divider and an attenuator?

A wider window of stability.

 

[Mikebits]

Copied from Wiki.

Attenuators are usually passive devices made from simple voltage divider networks.

Attenuator (electronics) - Wikipedia, the free encyclopedia

 

[Reloadron]

The problem you have is that your existing panel meters don't offer an analog signal out that is proportional to the input signal.

I am sure your current meter does not measure 600 Amps but is likely driven by either a CT (Current Transformer as mentioned) or a hall effect device.

Anyway, what you want to do is convert voltage and current signals you have to voltage and current signals you can use that are proportional to what you have. The conversion is easy depending on the budget you have to work with.

A Google of Ohio Semitronics or CR Magnetics will show you a host of transducers that would work for your application but devices like this aren't inexpensive or cheap. Is this a commercial application and what is the budget? The companies I mentioned are just examples but should give you an idea.

Ron