How to check the frequency meter

[metalworker393]

Hello everybody,hope everone is well.Okay,so I need some direction.I have one of my 003 gensets running,getting good oil pressure and no smoke.Getting 120 volts across both legs.Now my problem.How do I go about checking the frequncy meter and/or the transducer?The needle just hangs at the 55 hz mark like something is not working.
I would like to determine what exactly is wrong before I start wasting money on good parts if you know what I mean.
Thanks and appreciate anyone's help,metalworker393

 

[Keith_J]

I'm working on the answer. Basically, the transducer converts the frequency into a small current, between 4 and 20 mA. A tiny current but enough to swing the needle.

So my best guess based on the ranges of 55 to 65 Hz (10 Hz) and 4 to 20 mA (16 mA) would put the 60 Hz current at 12 mA.

You must remove one lead from the frequency meter and insert a milliamp meter to measure transducer output, never run the generator without the frequency meter connected since the transducer could be damaged.

The meter alone is over $100. Mine is water-damaged and I don't feel like rebuilding it.

As an interim measure, a hand-held tach reading off the crankshaft can be used. 1800 RPM of the engine is 60 Hz on the output.

 

[armytruck63]

If you have a DMM with a frequency function, you can measure that at the AC outlets.

 

[n1oty]

A quick down-and-dirty way to check the output frequency is to use a multimeter with a frequency readout. Most high end meters and many inexpensive meters have this feature.

John

 

[PeterD]

The transducer module is typically 120 volts in. Removing the wires from the module, and connecting to standard 120 house AC power will indicate 60 Hz if the frequency meter is working OK. Doesn't even require starting the generator set!

 

[metalworker393]

Frequency meter

Thanks for the help everybody,I'm getting 120 across the lugs in a 240 volt configuration so I'm thinking my engine speed is in the ball park.I'm going to ask my supervisor if I can borrow the companies strobe light to see how close the rpm's are.An electrician I work with said he will lend me a multimeter overnight to do this check too.Thanks again everybody,metalworker393

 

[rosco]

If your going to have a generator, you need a multimeter, so you can tell what is going on, with out employing the smoke test. You can set your RPM with the HZ function on your meter. If its at 55 HZ, crank up your throttle setting, and see if the HZ, on your machine, won't come up too. Then adjust your voltage with the fine tune knob.

The higher end meters are very foregiving. I just got a Fluke 375 clamp meter from Amazon, for $300 (free shipping). You can check the HZ at the 120V outlet. It checks currant, both AC & DC. You need the meter to verify the guage readings!

 

[Keith_J]

The transducer module is typically 120 volts in. Removing the wires from the module, and connecting to standard 120 house AC power will indicate 60 Hz if the frequency meter is working OK. Doesn't even require starting the generator set!

Good to know, I've traced the circuit diagram and see the same. This is but half of the frequency indication system, the other half is the meter.

My meter is corroded beyond what I can repair, the movement appears to be electrically intact (moving coil, permanent magnet) and since the transducer output is DC, simple DC resistance of the coil should give an educated guess as to the output of the transducer.

Common instrumentation uses variable current of 4-20 mA. The best measurement on my broken frequency gauge I can get is 550 ohms. This corresponds to about 6 volts. I will know soon what the actual voltage is.

 

[PeterD]

Keith, I've seen two different movements in these generators, so there is no 'standard' as such.

Were this mine, I'd connect to a knows 60 Hz source (house current is what I use, with a suicide cord) and measure the output voltage. A bit of Ohm's law and that will give current (since you know the meter's resistance it appears.) Once you have the current at 60 Hz, you then should be able to 'guesstimate' the full scale current without too much trouble.

 

[Keith_J]

Yes, Pete, there are two types of meters corresponding two different transducers. Mine is Technology Research Corporation of Clearwater FL, FSC 60177, model 72-5019, part number 10125.

My friend's 003a has the same unit but batteries were dead so no live test. But my ohmmeter worked as a variable voltage source and was enough to swing the needle full scale below 2k ohms and just had enough to swing the needle to 56 Hz on the 20k ohm scale. Now all I need is another accurate DMM to measure the current my DMM pushes in the 20k Ohm scale through a 580 Ohm resistor and I will have a good idea of how to make a digital frequency meter that is a drop in replacement. For about $10

 

[Speddmon]

Yes, Pete, there are two types of meters corresponding two different transducers. Mine is Technology Research Corporation of Clearwater FL, FSC 60177, model 72-5019, part number 10125.

My friend's 003a has the same unit but batteries were dead so no live test. But my ohmmeter worked as a variable voltage source and was enough to swing the needle full scale below 2k ohms and just had enough to swing the needle to 56 Hz on the 20k ohm scale. Now all I need is another accurate DMM to measure the current my DMM pushes in the 20k Ohm scale through a 580 Ohm resistor and I will have a good idea of how to make a digital frequency meter that is a drop in replacement. For about $10

If you have the knowledge and ability to make a digital drop in meter using the transducer output....why not just design one to do it all in one package and re-route the 120 feed lines from the transducer to the new drop in. If you could come up with a good looking drop-in digital meter for a good price there would be at least some demand for it.

I have no desire to play around with my frequency meters or transducers if they decide to go south on me. I will just replace them with a much more accurate digital meter...the only problem is, the only ones I've been able to find that are 120 input and inexpensive enough to be practical are rectangular in shape. I would love to keep them in the EOM round openings if possible.

 

[Keith_J]

Further measurement tonight on the transducer in my 002A showed 55 Hz at near 0 micro amperes, 60 Hz is 90 micro amperes and 65 Hz is 180 micro amperes. Far more sensitive than my digital frequency meter at 18 micro amperes per Hz. The transducer is a bit slow.

There is no way to retrofit to digital output without adding wiring, one of my goals. There just isn't any useful power to be had in the transducer output. Looks like I am forced to either go with a self-contained, 3-1/2" 120 VAC frequency meter. Or I could use the 24-28 VDC to power my $10 creation.