Digital panel amp meter
- Thread starter tdjs
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Analog meter
Analog meter
Analog meter
The typical analog current meter is a voltmeter in parallel across a calibrated current shunt. The meter reaches full scale deflection at 50 millivolts and the shunt is calibrated so that it drops 50 millivolts at full current flow. This is typical.
So in your example you may have a 100 amp, 50 millivolt, rated current shunt in series with the motor feed and a 50 millivolt voltmeter in parallel across the shunt with the dial marked 0 to 100 amps. The voltmeter is a match for the shunt and deflects full scale at 50 millivolt input to the meter.
The setup you have now may be a voltmeter measuring calibrated voltage drop across the shunt. I would look for the shunt and its nameplate marking to confirm this arrangement.
Going from this to digital, you probably have two choices:
1. A meter that uses the shunt in the same manner (calibrated full scale reading at 50 millivolt drop on the shunt).
2. An amp meter that does not use a current shunt, it would use CT's, current transformers that come with the meter.
If the meter is blown but the shunt is good, you may be able to replace with a matching meter knowing you are reading the shunt
Analog meter
Analog meter
The typical analog current meter is a voltmeter in parallel across a calibrated current shunt. The meter reaches full scale deflection at 50 millivolts and the shunt is calibrated so that it drops 50 millivolts at full current flow. This is typical.
So in your example you may have a 100 amp, 50 millivolt, rated current shunt in series with the motor feed and a 50 millivolt voltmeter in parallel across the shunt with the dial marked 0 to 100 amps. The voltmeter is a match for the shunt and deflects full scale at 50 millivolt input to the meter.
The setup you have now may be a voltmeter measuring calibrated voltage drop across the shunt. I would look for the shunt and its nameplate marking to confirm this arrangement.
Going from this to digital, you probably have two choices:
1. A meter that uses the shunt in the same manner (calibrated full scale reading at 50 millivolt drop on the shunt).
2. An amp meter that does not use a current shunt, it would use CT's, current transformers that come with the meter.
If the meter is blown but the shunt is good, you may be able to replace with a matching meter knowing you are reading the shunt
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SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Start by recording all the information on the present meter. It may be possible to find one that will fit the existing cutout.
Looks like your load is about 30 amps. I supect the existing meter reads that directly. Look for the End Scale on the meter information. Does it match the scale on the faceplate ? If the last number on the faceplate is the same as the ES then the meter is passing the load current directly through it's terminals. Another clue here would be the size of the conductors connected to the meter terminals.
A digital meter will require a source of voltage for it's power supply that the existing meter does not have. The same voltage that supplies the motor could possibly be used.
You may want to consider a combination type meter that can read voltage, current, watts, Power Factor, etc...
A supply house like Allied Electronics maybe could help if you have enough information from the existing meter. Our customer usually will specify a meter for us. Bitronics makes some nice looking meters.
Looks like your load is about 30 amps. I supect the existing meter reads that directly. Look for the End Scale on the meter information. Does it match the scale on the faceplate ? If the last number on the faceplate is the same as the ES then the meter is passing the load current directly through it's terminals. Another clue here would be the size of the conductors connected to the meter terminals.
A digital meter will require a source of voltage for it's power supply that the existing meter does not have. The same voltage that supplies the motor could possibly be used.
You may want to consider a combination type meter that can read voltage, current, watts, Power Factor, etc...
A supply house like Allied Electronics maybe could help if you have enough information from the existing meter. Our customer usually will specify a meter for us. Bitronics makes some nice looking meters.
There are a number of ways to do it depending on how the existing meter is connected. Possibly it is driven from a shunt as has been suggested, it may have its own internal shunt, or it may be driven by a current transformer which is how we normally do it.
Bear in mind that if you do use a digital panel meter, you will need to provide it with an auxiliary supply which won't be there for the existing analog meter.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
One other consideration is the stability of the reading. I would want a meter that has a bar graph + the digital readout. I have seen digital ammeters built into a motor protection relay. The current value would change every time the display was updated. It was difficult to read. That motor was connected to a ball mill.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
You may want to get a meter scale where the inrush could be watched. The motor on the ball mill I mentioned above also had 3 analog ammeters scaled so the full load current was about 80% of the scale. During startup the needles would look like a meter in a cartoon trying to spin around the dial 10 times. Since it was a reduced voltage motor starter this happened twice during each startup. Once when the START breaker closed, & again when the RUN breaker closed.
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