Digital ammeter "span" adjustment.

[driver0606]

A Happy New Year to you all.

I have replaced my boat's 0-60 amp digital ammmeter but the replacement while looking the same, has different number. There are two adjustable potentiometers, "Span" and "Zero" on the ammeter. The ammeter zero is correctly set and the meter indicates charge and discharge in the correct way except it always reads only about 10 to 20% of the true amount. The mA operating signal is so low, my multimeter cannot detect it.

Do you think I can turn the adjustment on the "Span" potentiometer, to show a more true amp reading, please?

 

[peteK]

It may need calibrating so perhaps that s what the span is,use a multimeter and compare readings.

 

[halcyon]

A Happy New Year to you all.

I have replaced my boat's 0-60 amp digital ammmeter but the replacement while looking the same, has different number. There are two adjustable potentiometers, "Span" and "Zero" on the ammeter. The ammeter zero is correctly set and the meter indicates charge and discharge in the correct way except it always reads only about 10 to 20% of the true amount. The mA operating signal is so low, my multimeter cannot detect it.

Do you think I can turn the adjustment on the "Span" potentiometer, to show a more true amp reading, please?

You are reading milivolts, not miliamps.

Shunt is normally something like 100 amp load = 75 mv signal, you need to measure the actual current, then adjust span to read the same.

Brian

 

[rogerthebodger]

You are reading milivolts, not miliamps.

Shunt is normally something like 100 amp load = 75 mv signal, you need to measure the actual current, then adjust span to read the same.

Brian

I normally use 100and - 100mv shunts so its simple to get a DVM that will read display 100 mV that becomes 100 amps.

Better is to get a all effect shunt so you don't have the volt drop in the shunt as well as the wiring particular when driving high current devices like bow thrusters or winlasses.

I got mine Hall effect shunts from a very nice gentleman from Cornwall some time ago

 

[halcyon]

I normally use 100and - 100mv shunts so its simple to get a DVM that will read display 100 mV that becomes 100 amps.

Better is to get a all effect shunt so you don't have the volt drop in the shunt as well as the wiring particular when driving high current devices like bow thrusters or winlasses.

I got mine Hall effect shunts from a very nice gentleman from Cornwall some time ago

Thank you, hope all is still well with them

Brian

 

[driver0606]

Thank you all for your replies and pointing out my measurement mistake. I will recheck. I presumed it was mAmps because the spec sheet from a similar looking meter by Murata, described it as having a "4-20mA current-loop-input". I presumed "loop" referred to the two wires from the also presumed shunt.
I am unable to find the shunt anywhere without stripping out large amounts of paneling and wiring, I think it was installed about 3 minutes after they laid the keel. The boat IS Italian!
I also read elsewhere that it was impossible to adjust ammeter readings upward, but perhaps that referred to an analogue instrument.
If turning up the "span" potentiometer can do the trick, I can certainly calibrate it with a multimeter. Does that sound worth a try, please?

 

[halcyon]

Thank you all for your replies and pointing out my measurement mistake. I will recheck. I presumed it was mAmps because the spec sheet from a similar looking meter by Murata, described it as having a "4-20mA current-loop-input". I presumed "loop" referred to the two wires from the also presumed shunt.
I am unable to find the shunt anywhere without stripping out large amounts of paneling and wiring, I think it was installed about 3 minutes after they laid the keel. The boat IS Italian!
I also read elsewhere that it was impossible to adjust ammeter readings upward, but perhaps that referred to an analogue instrument.
If turning up the "span" potentiometer can do the trick, I can certainly calibrate it with a multimeter. Does that sound worth a try, please?

If you only have light cable to meter then you have a shunt. a clamp meter would be useful to measure the current you need to set. Problem is you will only end up with an approximation, depends on measuring meter, how accurate it is calibrated. Can also be a problem due to meter design, it may not match the shunt .

Brian

 

[driver0606]

No problem. It is a 60 map meter and the cable is light, so defiately has a shunt. I have a clamp meter and some inaccuracy is acceptable. It may well be that the meter is mismatched. Isit worth trying to adjust the"span"?

John.

 

[greeny]

Thank you all for your replies and pointing out my measurement mistake. I will recheck. I presumed it was mAmps because the spec sheet from a similar looking meter by Murata, described it as having a "4-20mA current-loop-input". I presumed "loop" referred to the two wires from the also presumed shunt.
I am unable to find the shunt anywhere without stripping out large amounts of paneling and wiring, I think it was installed about 3 minutes after they laid the keel. The boat IS Italian!
I also read elsewhere that it was impossible to adjust ammeter readings upward, but perhaps that referred to an analogue instrument.
If turning up the "span" potentiometer can do the trick, I can certainly calibrate it with a multimeter. Does that sound worth a try, please?

If you increase the span, the reading will decrease. You will need to decrease the span and then re check the zero again as the adjustments are often interactive.

 

[driver0606]

I checked for Mvolts but there is no reading on the "loop wires". As there are also no detectable Mamps and the instrument gives logical but low readings, it must work by magic!
The instrument is new and described as reading to 60 amps and reads to a minimum of 0.1 amp. The "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading. . The "zero" potentiometer had a range of about +4 to -4 amps.

 

[rogerthebodger]

Did you check the Mvolt across the shunt with current being drawn from the battery with a multimeter

If you got a reading then check the "loop wires" at the meter, They should be the same if not you loop wires may be the problem if the reading is the same then meter could be the problem

 

[Bran]

Do you have the specification sheet for the ammeter you have fitted? If it is a 4 - 20 mA meter it will not work with a conventional shunt. Can you disconnect the ammeter and measure the shunt output directly?

 

[halcyon]

I checked for Mvolts but there is no reading on the "loop wires". As there are also no detectable Mamps and the instrument gives logical but low readings, it must work by magic!
The instrument is new and described as reading to 60 amps and reads to a minimum of 0.1 amp. The "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading. . The "zero" potentiometer had a range of about +4 to -4 amps.

Can you post a picture of the front and back of the display / ammeter you are trying to set / adjust, may help identifying your problem.

Brian

 

[driver0606]

I will try to get a spec. sheet. I cannot access the shunt. I have tried to include a photograph but whichever way I do it, it shows for a moment, then disappears and a message tells me there is a problem.
My question is -
The "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading . Does that indicate a faulty instrument, please?
John.

 

[PaulRainbow]

I will try to get a spec. sheet. I cannot access the shunt. I have tried to include a photograph but whichever way I do it, it shows for a moment, then disappears and a message tells me there is a problem.

Try reducing the image file size.

 

[Bran]

I will try to get a spec. sheet. I cannot access the shunt. I have tried to include a photograph but whichever way I do it, it shows for a moment, then disappears and a message tells me there is a problem.
My question is -
The "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading . Does that indicate a faulty instrument, please?
John.

Faulty instrument, failed shunt, incorrect instrument, faulty wiring. Could be anything. Can I ask a few questions? Let’s go back to the beginning, why did you change the ammeter display? What type was the original ammeter? What type is the new ammeter?

 

[halcyon]

I checked for Mvolts but there is no reading on the "loop wires". As there are also no detectable Mamps and the instrument gives logical but low readings, it must work by magic!
The instrument is new and described as reading to 60 amps and reads to a minimum of 0.1 amp. The "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading. . The "zero" potentiometer had a range of about +4 to -4 amps.

What are you describing as ..... "loop wires". ? thick wire loop on the back of the meter, or wire connecting to meter ?.

Brian

 

[driver0606]

The old ammeter worked well for a number of years then went haywire displaying random, continually changing readings. The yacht builder, Azimut supplied the replacement which works perfectly, except the readings are too low. There is no maker's name on the meter.

There are 4 wires connected to the meter. 2 wires are the 24v supply. I use "loop wires" to describe the other 2 wires that bring the signal into the meter.

All I want to know now is the new meter probably faulty because the "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading. The "zero" potentiometer had a range of about +4 to -4 amps.

John.

 

[halcyon]

The old ammeter worked well for a number of years then went haywire displaying random, continually changing readings. The yacht builder, Azimut supplied the replacement which works perfectly, except the readings are too low. There is no maker's name on the meter.

There are 4 wires connected to the meter. 2 wires are the 24v supply. I use "loop wires" to describe the other 2 wires that bring the signal into the meter.

All I want to know now is the new meter probably faulty because the "span" potentiometer was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading. The "zero" potentiometer had a range of about +4 to -4 amps.

John.

The problem is you are not seeing any voltage on "loop" wire, or do not appear to be, so it could be meter or feed to meter.

If you disconnect the meter, turn on some loads do draw say 20 amp,

do you have a mv reading on the meter ? you are checking for shunt voltage

if you put the multimeter positive probe on the 24v supply and neg probe on each "loop" feed wire in turn do you get a correct voltage reading ? will check for a continuity of connection to shunt.

no voltage reading ? try neg probe on neg supply and pos probe on "loop" wire, shunt may be in pos supply, not earth power supply.

Brian

 

[driver0606]

Thanks Brian,

I will try that and report back.

Do you think the "span" potentiometer may be faulty because it was turned throughout its range but the maximum change in reading was only 0.1 amps on a 5 amp reading?

John.