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Posts: 599
Reply with quote  #1 
So here is a weird one for you. I have only gotten a tiny bit of information, but I thought I'd start with putting a feeler out here.

Client has a BN 177230 accel (4-20mA output). Vibration is low. However, when they use a 2-way radio (walkie talkie) near the pump and switch from listen to talk mode, there is a current spike and the pump trips as a result. This is a reproducible effect.

I cannot think of any mechanism or failure mode for how this would be possible.

John from PA

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Posts: 963
Reply with quote  #2 
The device itself complies part 15 of the FCC Rules. Operation is subject to the following two conditions:

"This device may not cause harmful interference" and  "This device must accept any interference received, including interference that may cause undesired operation."

In my experience 2-way radios rarely cause issues and when they do it is usually traced to the system wiring going back to a monitor or readout device.  Having said that it is not impossible to have a defective transducer that may be prone to the problem.  Do you have another transducer that you can swap out to judge the effects?  Is this device routed to a monitor and if so what type/model monitor?

As far as wiring Meggitt/Wilcoxen has a good paper on installation that discusses the issues.  See, specifically page 7.
Danny Harvey

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Posts: 1,403
Reply with quote  #3 
I'm not sure if this experience is really applicable but I found that when using CSI 2120 with a 628 2-channel adapter and recording PeakVue data while using a tunable strobe, the strobe will appear as sharp spikes in the twf and dozens of harmonics of strobe speed in the spectrum if there is a problem with either of the bnc connectors.

I never knew why this happened and I haven't had the problem in about 20 years since CTC started supplying me with cables that don't have bnc connector failures. Prior to that, it was the easiest way to find that yet another CSI cable had broken. One about every 6 weeks or so.
Walt Strong

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Posts: 889
Reply with quote  #4 
Does the sensor require 2-wire twisted pair with shield? Typically the shield is floated only at one end.

I only encountered radio interference on vibrations a very long time ago. It was a B&K accelerometer monitor setup in control room on a instrument rack about shoulder high. Any time the radios were used with antennae nearby, it would trip the ID fan. The monitor had a plastic front panel, so RF shielding was poor. I put a piece of aluminum foil behind the panel and it worked well.


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Posts: 1,917
Reply with quote  #5 

Running Bently signal cables beside hi amp VFD motor wiring for 15-20m and then wrapping the rack and cable inside the container/control room did not improve signal to make it useful.
So there are levels of problems.
As a producer of converters that output 4-20mA signals, interference on the 4-20mA side are rare. I can't say I ever had to suggest screened cable for that as the information is carried by the 
current and normal induced interference is a voltage. Anyway grounding principle also of 4-20mA native sensors may give trouble. If the case the transducer is grounded and is the same as one side of the 4-20mA signal current loop you may have a significant current flow along the full length of the cable that give trouble but it would normally be like it trip when lube oil pump start or so.
I have had a case where a slave rely was sensitive for com radio RF, a screen i front of the cabinet solved it.
So there must be a feature that act as a receiving antenna, maybe trying to mount the sensor on a electrical isolating pad is something to try? Also verify that the connection in the other end is as OEM describe.

Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.

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Posts: 163
Reply with quote  #6 
Probably because it is Alexa-enabled   [biggrin]

sorry,    I couldn't resist


Posts: 3
Reply with quote  #7 
Stabbing in the dark here, as you don't give details on how the system is configured, wired or how low the normal signal is. So a number of possible causes. As others have suggested, transducer or wiring faults are not unusual to find - connectors can be especially problematic especially is they are wired on site.  In my experience BN accels /velometers are not the most reliable of those available.  I have seen radios (and lightning ) cause trips on VA systems, and it has invariably been found to be a grounding issue or fauly accels, but I have not seen this on a 4-20ma systems.
These velometers put out a dynamic signal and a overall - Is the correct one wired back to your instrumentation? Overall is used to trip/ monitor and the dynamic to analyse. One possible configuration is that you can wire the dynamic back to a BN system 1 and use the BN System to trip as well as monitor.  The following assumes this is what is happening. In my involvement in auditing and commissioning BN systems I found many errors in programing of System 1,  especially where velometers are involved. It is not uncommon to find someone had assumed the signal was from an accelerometer and integrated it to velocity thus, in effect, performing a double integration. Usually this gives a very low vibraition indication but very susceptable to any form of spike - perhaps from a radio. 
As a critical system should not normally have a single accel or vel. as a trip, I assume it's not a critical pump, therefore a work around is to change the trip delay to >5 seconds or so. This was how we dealt with non critical pumps with trips in 1oo1 configuration where spikes were created by other nearby equipment starting up - in preference to raising trip levels .
Good luck

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Reply with quote  #8 
Thanks everyone for the feedback. I guess it makes sense that the voltage signal would be more susceptible to EMI than a current loop.

As Andy pointed out (welcome to the forum!), it may well be that they are using the voltage output in parallel and have a trip thats not actually on the 4-20 monitor, but on some other monitor.

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Posts: 88
Reply with quote  #9 

Since there is a dynamic out on the sensor, connect a portable analyzer to it and trigger a radio, that will tell you if it is the dynamic signal (most likely) or the 4-20ma (doubtful) that has the issue.

The wiring on this is a little weird as you will have the common shared across two systems, verify the wiring, especially the grounding of the shields as others have mentioned. 

Is it just this unit that is having issues?  Do you have a similar set up on any other machines?  I'm a firm believer is Sesame Street analysis, compare the wiring and configuration and if one of these things is not like the others, its probably the problem.

I'm assuming you tried swapping out the sensor?

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