Little help with motor load meter spec?

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fastline

Member
trying to replace a motor load meter. The meter runs off an output from a Yaskawa VFD. The current load meter works but has damage and is hard to read. It indicates 0-10VDC and terminals have 10kohm resistance.

https://www.ebay.com/itm/GE-Panel-M...=item3fb3ce515e:g:CiUAAOSwsRVcCsI-:rk:15:pf:0

I am considering this meter as a replacement but cannot find any specs on it. However, the label says 0-100 uA and when I do the math on the 10V scale against my 10ohm meter, that would be 100 uA at 10V. There is mention about 825ohms though so I don't understand that.
Any help would be appreciated!

ronsimpson

Well-Known Member
It indicates 0-10VDC and terminals have 10kohm resistance.
That gives me the idea your old meter is 1mA.
when I do the math on the 10V scale against my 10ohm meter,
???
There is mention about 825ohms though so I don't understand that.
If you measure the new meter with a ohm meter it will have a resistance of 825 ohms.

If your "VFD" outputs 0 to 10 volts then you need to make a 10V meter. (1mA or 100uA will not matter to the VFD)
Try removing the little board from the back of the meter and add a 100k resistor in series with the meter. That should make a 10V meter.

10V/100k=100uA

fastline

Member
I don't own the new meter yet as I am uncertain it we (your help) can make it work? Also, I do not understand the 100k resistor? In series, that would be much higher than the other one? I might need to understand these better. Some say they look at current, some voltage but ultimately as voltage goes up on a fixed resistance, so will current.

What I meant earlier is if you take to max voltage/ the internal resistance of the oem meter, that is 1mA.

ronsimpson

Well-Known Member
My guess is that the new meter will use 1/10 as much current to move the meter as the old meter. That is probably OK.
Do you have a volt meter? Some thing that can measure the car 12V battery.
I think if you use a multi-meter and measure the VFD output it will read 0 to 10 volts.
Then we need to change the new meter from a "100uA" meter to a "10 volt" meter. The purpose of the 100k resistor is to get 100uA at 10 volts.

Here is the schematic of a very simple A and V meter. Lets say it is a 100uA meter. There are three "V" settings, using three different resistor values. Maybe R1 is chosen to get full scale readings at 1V, R2 for 10V and R3 for 100V. (R3 value is so at 100V you get 100uA of current)

fastline

Member
Ah. Next question would be how these work when the meter is designed to read overload? All these VFDs/motors are designed to handle overload S/3, S/6, etc so very normal to see 125-150% of continuous load. How does that work with the meter? Is 10V set to be 200%? Will the voltage from the VFD exceed 10V in these overload cases?

rjenkinsgb

Well-Known Member
With a simple voltmeter running from the drive, the "overload" scaling is done in the drive and it's just the meter scale that is customised.

Maximum needle deflection on the meter will still be 10V.

For information, With ammeters, there are both linear types and non-linear ones designed for higher overload situations.
eg. This one uses a fraction of the scale for double the current:
https://uk.rs-online.com/web/p/analogue-panel-ammeters/0202782/

Possibly more relevant, many square-style industrial meters have removable scales so the scale readings can be made to match the application, regardless of what voltage or current the meter movement itself works on.

If you need a specific scale layout, one of those may be suitable?

These are just some of the scales you can get for that style of meter:
https://uk.rs-online.com/web/c/auto...omponents/analogue_panel_ammeter-scales/?pn=1

If there is nothing suitable, it's possible to carefully remove numbers from one that has suitable scale divisions using metal polish and put new markings on with letraset / rub-down lettering..
I've done that a few times when rebuilding machines, you just have to be careful to not go through the white background near the characters you are removing...

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