NOS Dealer Installed CC FORD F2TZ-9A818-A

[evL]

I think you may be onto something. You won't see the full voltage of a pulsed signal with your meter on the DC scale. At best you'll see an averaged voltage, meaning that a signal that has a 10% duty cycle pulse may read ~10% of the DC value.

I'll go to the shop again in a bit and look at my '96 EVTM to see what it says, if anything, about duty cycle. But you might try reading it on the AC scale.

I remember reading somewhere it was an AC voltage, I think a sine wave, from the rear differential to the PSOM but the PSOM puts out a different signal from pin 6. Regardless I'll check tomorrow.

[Gary Lewis]

I remember reading somewhere it was an AC voltage, I think a sine wave, from the rear differential to the PSOM but the PSOM puts out a different signal from pin 6. Regardless I'll check tomorrow.

That page from the 1996 EVTM, above, says the PSOM converts it to 8000 pulses per mile. So it isn't a DC voltage. Instead, it is probably something approaching a square wave, not a sine wave, since it is far easier with solid-state electronics to create an on/off signal than a shaped wave.

Surely the pulses are sufficiently narrow that the vehicle can do 150 MPH w/o the pulses running together. So if we assume 150 then at 30 you have a 20% duty cycle and your DC voltage might read something less than 1 volt, and maybe less if the duty cycle is less. But, many volt meters don't like pulses and give wonky results on the DC scale.

Your meter might give reasonable results on the AC scale, but it might not as these probably aren't sine waves and aren't coming at 50-60/second, which is what most meters expect.

I think the only way to truly know what you have is to look at the signal on a scope. But those are rare these days, and most don't run on batteries so you can't take them up to 30 MPH - unless you have a really long cord. However, the fact that your meter is seeing something is encouraging and says you have a signal. But I'd try it on the AC scale to see what you get.

[Steve83]

Isn't a True RMS for accurately measuring standard [pure ac] sinusoidal waveforms?

No, true-RMS is for measuring AC voltage or power on anything OTHER than a 60Hz sine wave.

Now I might be completely off because I was measuring DC not AC. ?

That's why you're not reading the signal that has probably been there the whole time.

...on the DC scale. At best you'll see an averaged voltage...

The average of an AC signal is only the DC offset, which is usually 0V (ground). Duty cycle has no impact on the DC reading of an AC signal.

I remember reading somewhere it was an AC voltage, I think a sine wave, from the rear differential to the PSOM but the PSOM puts out a different signal from pin 6.

No, it's a Hall-effect sensor - not a simple inductor. So it puts out a nearly-square wave. The PSOM's output is probably slightly closer to square, but it doesn't really matter. Use a true-RMS meter set to ACV.

[evL]

Isn't a True RMS for accurately measuring standard [pure ac] sinusoidal waveforms?

No, true-RMS is for measuring AC voltage or power on anything OTHER than a 60Hz sine wave.

Now I might be completely off because I was measuring DC not AC. ?

That's why you're not reading the signal that has probably been there the whole time.

...on the DC scale. At best you'll see an averaged voltage...

The average of an AC signal is only the DC offset, which is usually 0V (ground). Duty cycle has no impact on the DC reading of an AC signal.

I remember reading somewhere it was an AC voltage, I think a sine wave, from the rear differential to the PSOM but the PSOM puts out a different signal from pin 6.

No, it's a Hall-effect sensor - not a simple inductor. So it puts out a nearly-square wave. The PSOM's output is probably slightly closer to square, but it doesn't really matter. Use a true-RMS meter set to ACV.

Great info guys...

Gonna find a True RMS meter and give it a go on AC...