I have some upcoming work on a machine with a vintage late-60's or early 70's IRD rack and non-contacting proximity probes. I seem to recall that back then IRD had a strange scale factor, not the "typical" 200 mv/mil per API spec.

Anyone remember what the scale factor is?

Thanks,
John

Around that time, didn't Bently Nevada make the proximity probes for IRD? If so, you may be able to check in house.

Before 1971, IRD used a shielded probe that, as far as I know, was not made by Bently. It had a shorter range than Bently's but supposedly was much sturdier than the Bently probes of the same era. I installed a few of those systems but I don't remember the sensitivity although I think you are correct in saying that it wasn't 200 mv/mil. In that era, Bently had some probes with other sensitivities which I remember because I installed Metrix Datawatch monitors on a set of power plant pumps that came with Bently probes and proximotors and had to modify the Metrix hardware because they were set for 200 mv/mil only.

John,

Do you know what rack it is?? I may be able to help if I knew the model number of the rack or probes, either one.

Dave

I don't think it was the probe but the instrument. 200 mV P-P or 100 mV 0-P by rms or 70.7 to correct the EU to 1 mil. So you should be able to use 100 depending on the instrumentation you're using now. Don't tell me you're using a SD-240.

I also remember IRD racks of that vintage having positive gap voltage rather than negative. I don't remember scale factors, but I do remember having to mess around with scale factors till I found one that matched to monitor scale....

John,

I am going to assume you are working with what would certainly be obsolete racks, so I will list a couple of the factors for you for different systems. The calibration factors assume a target of 4140 steel. This factor, as you know, will change with different materials.The probe, extension cable, and probe driver were usually ordered together as a system, and calibrated as such using the dial indicators and a target.

The 403-250 NCPU, has a sensitivity of 60 mV/mil. 200 mil gap nominal. It uses -24V power supply.

The differential expansion system, PN 26400 and 26401 (pickup and power supply/sensor),150 - 650 mils gap, has a sensitivity of 30mV/mil. -24V power.

The signal sensor (probe driver) #8695, which was used in the 70's with a NCPU provided the signal to several different manufacturers monitors. It operated on +24V from the monitor, and had a sensitivity of 200 mV/mil.

The sensor (probe driver) #5362 had an AC output of 240mv RMS/mil pk-pk, and used +24v to power the sensor. About any NCPU would be hooked to it.

There are many combinations of probe,signal conditioner/power supply that were used. SOme of them were special order, some were standard.
If you can come up with the numbers, I may be able to help further.

Thanks,

Dave