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How to interface Analog Panel Meters?

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howie

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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
 

keith1200rs

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The current meter will have probably have a shunt resistor built in, so you will probably need to measure a small AC voltage there. Put a multimeter in AC voltage range across the ammeter and see what you measure.

The problem with a bridge rectifier will be accuracy due to the diode volts drops. It will not be too far out at 600V but may be poor accuracy measuring across the ammeter shunt.

An active rectifier would be more accurate:

https://en.wikipedia.org/wiki/Precision_rectifier

Keith.

Added after 41 seconds:

Also, there are "true RMS" measuring chips which will take account of the waveform shape if it isn't a true sine wave.

Keith.
 

srizbf

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for the voltage and current specifications ,
you must use 'pt and ct's only.
(pt-potential transformer and ct-current transformer)

in the secondaries , include all your electronic methods .
no other way.

srizbf
3rdmay2010
 

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