# How to "fake" a megawattmeter

I have a vintage megawattmeter. It is able to indicate values from -1 to 7 MW. I wish to be able to provoke it to display any value I want, preferably without actually generating megawatts of power.

If I understand this correctly, it means that both power and voltage are transformed down, from max. 1000A to max. 5A, and max. 6000V to max. 110V. The first symbol seems to indicated that two phases out of three are used for the measurement?

There are 7 Connections on the meter, numbered from 1 to 7. If I understand the diagram correctly, this means that connection should be like this:

1. phase 1 current in (k) - low voltage
2. phase 1 voltage - low current
3. phase 1 current out (l) - low voltage
4. neutral
5. phase 2 current in (k) - low voltage
6. phase 2 voltage - low current
7. phase 2 current out (l) - low voltage

What would be a good way to control this meter to display my desired values?

I was able to open up the instrument. As far as I can judge, connections 1 and 3 go to one big coil, 5 and 7 go to the other big coil. Connection 4 goes to the chassis of the big coil that has the needle. Connections 2 and 6 go to each of the two smaller coils, and from each of the other ends of those coils, there are wires to the needle mount and the moving element in the other big coil. See pictures below. I'm still not sure how I Shield proceeed to get it to actually show the values I want.

I tried to measure L and R. Wasn't able to find C.

• Across 1-3 R 0.3 ohm L 0.5 H
• Across 5-7 R 0.3 ohm L 0.4 H
• Across 2-6 R 1878 ohm L -4 H
• Across 2-4 R 225 ohm

• Open it up and look for the needle assembly. Disconnect it and test what current you need to make it move. Sep 12, 2017 at 7:57
• What do you excpect the needle assembly to look like? Is it likely to have only two connections? Should I supply AC or DC? Sep 12, 2017 at 8:37
• Just similar to the needle assembly of any analogue meter, a coil that drives a needle, very likely DC Sep 12, 2017 at 8:45
• Clearly you need high current (at low voltage (1)) and high voltage (at low current(2)), both at 50Hz, and 2 phases 120 degrees apart. First, measure some impedances (both L and R with an LCR meter) to establish (1) and (2). Then get hold of an audio signal generator, some passives to make a phase shifter (or Audacity again), a cheap stereo amplifier, and four cheap mains transformers. Step up for voltage, down for current.
– user16324
Sep 12, 2017 at 10:14
• Appreciated. I ordered an LCR meter and will measure when I next have access to the hardware. The Audacity solution worked well for my frequency meter. In this case, will four 2A transformers with ~20 ratio (intended for 230VAC->12VAC, 24VA) be suitable? I would be able to work from a supply with a little more than 5V and 50mA per phase (ignoring losses)? Sep 12, 2017 at 22:47