Weston 545 Tachometer

Did you find it?

No, I did not. That is why I am seeking help.

The information I needed was kindly provided by Pacific Southwest Instruments!

My thanks to them in helping to further this rebuilding process.

So they did come through! Can you share with us, in general terms, how it's done? Thanks for letting us know the final outcome.

All the more reason to ban anonymous posters!

The tachometer systems used on the planes I worked on had a mechanically driven tachometer generator that worked in conjunction with the indicator. Do you have the generator as well?

The generator is still on the boat. All I have are the tach indicators. They appear to have coils wound with a specific amount of wire that, I assume, are used to calibrate them. If I can find the procedure, I will either wind new coils or substitute precision resistors.

If you can remove the generator from the engine and drive it with a known rpm perhaps there is a calibration function on the indicator.

The Pratt & Whitney system used a three phase PM generator and the indicator used hysteresis slip to drive the needle.

It seems that this instrument is just a voltmeter that is used with different faces for many different applications. I have one that is functional and that is the way it seems to operate.

The ones for the PT boat are exactly the same as the ones on aircraft. I tried to get a company in California to provide some information, but they feared that the FAA might not approve of it. As the PT boat does not fly, I can't understand the logic. However, they are part of the government and don't have to make sense!

I had found a manual on EBay, but it is no longer available and I have not been able to locate anything additional. As these were used in many aircraft of the WWII era, I was hoping someone would still have access to the procedure.

Have you tried contacting other groups having similar interests for this information?

Actually, he did! And got better info .

I think the company is Westcon. If you Google 'westcon tachometer generator' and 'westcon tachometer indicator', you may find something. I think the company now is Marsh Bellofram. Here's a basic diagram. As someone else said, it's probably a DC voltmeter. The only adjustment I can imagine would be to zero the needle and possibly a calibration pot on either the indicator or generator. Is one visible?

It would be easy if it were actually a Westcon that is now Marsh Bellofram as I work for that company! The model is 545 and the only other information on the dial is:

Model 545 R T-82P. There appears to be a serial number, but it is not legible.

That's what I get for thinking .

What is the list/series number for that meter? It should be on the meter face, bottom left or bottom right. If not visible behind the glass, removing the bezel might be necessary.

Model 545 R T-82P. There appears to be a serial number, but it is not legible.

I have a different version...probably slightly newer. Can't seem to locate the test specs right now.

The one functional indicator I have takes a 0 to 10 VDC signal to indicate 0 to 3000 RPM. The response appears to be linear also.

I would take that information and bounce it off of the sending unit. Use a tach/counting meter or calculate the gear ratio to supplied voltage.

Since your gauge is working (linearly--nice!), I'd say you are more than halfway there.

If the indicator is in fact a volt meter and you can either run the engines or simulate running at the tach generators and know the actual rpm, You should be able to adjust the voltage (either by the precision resistors you mentioned or precision potentiometers) until the indicators read the actual rpm.