Created Date: October 21,2011

Created by: pressgrove

I have some I used for some testing. I used the current sensing ones because I needed to hook them to a data collection device instead of a PLC, and the data collection unit I had could accept current inputs only (and I generally prefer them anyway).

The only issue I had with the analog prox sensors was that the signal is not linear. If you are using them for relative measurement, this is not a problem. You can just see what your input is at known distances (or your outer spec limits). If you want them for absolute distance (like I did), it's a little more complicated to scale them. I ended up stacking pieces of plexiglass as spacers to get a signal value at known distances and plotting the signal values in Excel. I then let Excel best-fit a curve to the points. (I ended up dumping the values at the absolute ends of the sensor range to flatten out the curve). The more points you use and the more complex the formula, the more accurate your scaling will be. I then used the formula to scale my signal values. If you are using a P3000, there is a box command that will do non-linear scaling. It works similar to what I described above.

As for your question about current vs voltage sensors, it really depends on what you want to do and the environment. Voltage sensors are easier to read with a meter because you don't have to disconnect wires to get a reading. That said, if you use terminal blocks with disconnects for your signal wire on a current sensor, you can just use it to put your meter in series with the signal without unwiring anything. Again, if you are using a P3000, the voltage is displayed on the LCD on the input card, regardless of the signal type. Voltage signals are more suceptible to noise since stray voltage can actually alter your signal slightly. Personally, I use current signals more often because they are available on more devices than voltage and it keeps the maintenance guys from having to worry about the signal type.

Created Date: October 21,2011

Created by: Adisharr

Hi Everyone,

I am looking at using an analog prox. sensor for checking the runout on tubing. With that being said I am wondering what the differences are to using a voltage output versus a current output sensor. Thanks in advance for the help.

Voltage outputs tend to be a little easier to troubleshoot due to easy monitoring with a voltmeter. They also are more susceptible to noise. They require a high impedance input. Long cable runs can affect readings due to the potential for voltage drop.

Current outputs are just the opposite. Harder to troubleshoot due to the need to break the circuit to get a reading. Better against noise and require a low impedance input. Not affected by cable distance as long as it remains under the impedance limit.

Created Date: October 22,2011

Created by: pj.meza

I personally use current sensor (4-20ma), reason beside the ones share by others:

If a broken wire or sensor fail , then 0ma will be in the input and this will be consider an alarm. Even, this might be also be programmed with the voltage sensor. I prefer the current sensor.

I normally state in my drawing the input resistance in the PLC or module. Or the mV range V=IR. V(mV)= 4ma x R and V(mV)= 20ma x R. This helps to easy check the sensor.