330525 GAP VOLTAGE SETTING

Gap voltage is usually set at 9V with a plus or minus of 0.1. It doesn't have to be prefect as the vibrations give your change in indication.

usually -10V for bently naveda 3500system. it may not be correct to take mid point because of linearity and mystem requiremnt. The -10V is arrived by leaving -2V both side.

Hi Joseph

I am not sure what you mean by "Going through a P&F barrier?

But, the gap voltage is preferably -10VDC and the reason for this is as per below

1. The supply voltage is -24VDC and the usable linear voltage is between -2 and -18VDC

2. The above is based on the fact that the sensor output linear response is between -2 and -18. As you may be aware, the sensitivity of your sensor is 8mV/micronM.

3. The above mean that the gap voltage change of 1/1000mm or 1micron will give you 8mV DC gap.

4. Therefore, looking at our linear response of between -2 and -18V, one would like set ones neutral/zero position of the probe midway either side (sensor far or nearer to the shaft).

This point is - 10VDC.

Regards

Ephraim Tekete

Ass. Div. Engineer Condition Monitoring

Sappi Saiccor (Pty) Ltd (Reg.no.1989/001135/07)

Phone: +27 39 973 8199

Fax: +27 39 973 8805

Mobile: +27 83 236 1081

Mail: Ephraim.Tekete@sappi.com

Hi Joseph

For bently nevada 3500 system set the gap voltage at -7.5 to -10 vdc. but if you go towards -10 then you are at the end of the linear area and near the knee, as you go out the linearity drops rapidly. ideal is -7.5 where you are at around 35 mils and its the best spot to be on. You get pretty accurate values here.

regards

Naveen

Naveen,

I am not sure what model of probe you are using, but for most Bently probes, and for the 3300, systems -10VDC is the center of the range, and the linear range is typically from about -2.5 VDC to about -20 VDC.

A gap set for -9 to -10 VDC is fine for a radial probe. For a thrust probe you need to be careful how you set things up. Depending on how much float you have in the machine, a standard probe may not have enough range. We often zero on the active thrust shoe to accomodate range issues.

Hello Steve..

Iam using 3300 NSv system. for centrifugal compressors and also for turbines.I also use other systems . I find good results at the gap volt of -7.5VDc to say -10Vdc, and with my observations i feel that -10.5 is the max you should go up and that you are on the knee.

regards

Naveen

I am sorry, I am still not sure what 'knee' you are talking about.

If you look at the bottom graph you can see that the prox output is linear from about -2 V to about -16V, if you graphed it out further you would find it is still linear to about -19 and then the curve starts to roll off.

Prox probes are designed to operate anywhere in this linear range. We typically try to gap in the middle of the range, about 45 to 50 mil and -9 to -10 VDC only so if there is a big vibration (on the order of 70 mil pp) that the output remains linear.

If you knew that you would never see a vibration over a couple mils pp, you could gap at say -3 VDC and see very little error. In fact the need for the linear range is not for radial probes, it is so radial and axial probes can be interchangable. Axial probes may well need every bit of eighty mils linear range.

It should be installed such that gap voltage shows -10V DC while shaft is at rest.

Is there any significance for the eddi current in the gap voltage setting?