Walkie talkie near PLC

  • Thread starter rajesh kunhi kambrath
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rajesh kunhi kambrath

can the signal from a walkie talkie radio erase the contents in a PLC processor if we operate the same near by.

Christian Felde

I know mobilephones using the GSM network can interfere with hi-tech equipment because of the high frequency it's transmitting on. So may be if the frequency if high enough on the walkie talkies.
I have experienced all sorts of weird problems with the memory in a Motion Controller being corrupted as a result of RF interfernce. I would presume that the PLC is also subject to same.

Sharma, Anand

Mr Rajesh, The magnetic force exerted by the magnet decreases by the second power of the distance and hence if the distance of the magnet doubles means that the force exerted by the magnet decreases by one fourth. So your question depends on how close you intend to bring the walkie talkie to the PLC processor. But since most of the radios are shielded themselves IMHO a PLC processor won't be affected by it all. We have seen PLC's working in hazardous conditions like near cables carrying kilos of voltage. And even the electrostatic and electromagnetic shielding of the PLCs used in process industry are so rugged that a coin sized magnet of the walkie-talkie does not affect at all. If the PLC processor is completely unshielded then the charge accumulating on the PLC chassis (say, due to contact with human skin) and that of the earth's magnetic field should be enough to damage it. I hope this helps. Anand Sharma Tata Consultancy Services SEEPZ, Mumbai Ph: 91-22-829 0162 (ext-253) [email protected]
Hello Rajesh, We use GE-Fanuc Plcs. We have used motorola GP-300 Walkie-Talkie sets very near the racks. As much as 1 meter near them. As of date we have not experienced any problem. But we have experienced problems with analog circuit boards installed in field control panels. If a walkie-Talkie set is used within a metre or so the circuits go haywire. Should be the poor emi-rfi shielding on the boards. Tomy Zacharia Instrumentation Engineer

Ricardo Ribeiro

Dear Mr. Kambrath, I've seen situationd where this was VERY criticall. Never do this inside analog cubicles; that's the rule of thumb I use (I've scrapped a billet in a steel plant when doing this. I was lucky nobody got hurt!). I've done some tests inside PLC cubicles and it worked fine. But I don't trust! Be at least 2m away. Stay behind the cublicles door. Bye, Ricardo Ribeiro

Patrick Beckett

We have seen a walkie talkie affect the PSU of a PLC, tripping the PSU and then require a power cycle to reset the power supply. This we have seen on the Allen Bradley 1746-P2 power supply. But we have seen other instruments be affected by walkie talkies, including proximity switches and 4-20mA loops. However, we have never had a cpu be corrupted by them, at least, not yet (cross fingers & touch wood). Our problems only occured when the radio was within 2 feet or so. Regards Patrick Beckett Merlin Systems Limited
I have not seen it erase the contents of the processor, but I have seen it cause faults that took down the equipment. Electricians using handheld radios near an open panel would fault the PLC, but the same radio at the same place with the cabinet closed was fine. Ed M. Speaking for me, not for Starbucks.


I am confused by the reply. A walkie talkie is inherently unshielded, isn't it? At my former employer, we had a few PLC memory dumps that were mysterious and could not verifiably be traced to our 2 way radios. However, I can say that when it came to the circular chart recorders (ABB) and our loop controllers (Honeywell), keying the microphone within 5 feet of the panel created enough induced noise that the controllers would go upscale, causing a failed batch. This was 100% repeatable. We tried grounded screens, etc. to protect the devices, but even then, anything within 2 or 3 feet would corrupt the controllers. Final solution? Tape off an area on the floor with a "No Radios" zone around the control panels in question. As I said, we never had a *repeatable* case of corrupting a PLC processor, but it is something to be wary of. Just to clarify, it was not the tiny magnet in the speaker of the walkie talkie, but the transmitted radio signal that caused the problem. --Joe Jansen

Pierre Hinse CET

My experience has been, the RF gets into your analogue and digital inputs, more so if they are high impedance, resulting in weird levels and voltages/currents. This causes unpredictable results with the PLC program. The result is the same, your process control is broken.
At a site I was working at, we were commissioning IO on a TI545 and while using Motorola G300 radio's, the V-memory got scrambled. The radio was close to the processor and rack approx 500mm, since then we have procedures in place that radio's have to be outside the cubicles, and remote microphones/speakers are fitted. The existing analogue systems were quite sensitive, especially thermocouple devices, but the cables weren't shielded. Regards, Trevor Ousey

Bob Desrochers

I ran across this once a couple years ago. An AB 5/60 running a process and an unsuspecting electrician keyed the (FM) walkie talkie next to the cabinet with the door open. This processor previously had 3 yrs of runtime without a single fault. As the unit was keyed, this processor faulted and corrupted the memory and configuration settings. I had to clear the memory and start from scratch to get it up and running again. I'm not sure if the PLC or the power supply fell victim to the RF but the result was just as nasty. Bob

Donald Pittendrigh

Hi All I have not seen these problems happen with a Siemens PLC since the very early 80's, when I have experienced a case where interference induced onto an interface cable plugged into the CPU and open on the other end, caused a malfunction of the CPU. I would like to point out a bit of a generalisation that if the memory area in which the PLC builds its memory map of the blocks in RAM, is corrupted, the PLC is as good as erased, it is highly unlikely that interference caused by any radio device could emulate an "ERASE ALL" command in any PLC. Now for another one, the automation industry is very keen on installation of SCADA servers in panels near PLC's, industrial PC's are noisy things and the greater majority of them are standard desktop hardware in hardened cases. Most of the hardened cases I have come across were designed more than 12 months ago, when CPU's didn't run at much above 500Mhz, I have PC's such as this that interfere with my clients walky talky radios, such machines are also capable of interfering with PLC's, and they run at similar speeds to PLC hardware, so the likelihood is quite good that an accident will occur. I have found a supplier who makes a box rated for FCC regs. above 500Mhz, the difference is noticeable in practical terms, I have made no efforts to measure the difference, so those of you who propose to upgrade old systems or install new hardware in old 19" racks in your PLC control panels..... watch out..... Murphy has got his eye on you. Regards Donald Pittendrigh

Darold Woodward

You should check with the mfr. to determine if there is a specification for incoming RFI interference. Because PLCs are generally open frame and intended for back panel mounting, you should expect them to be vulnerable. The enclosure (ferrous metal and properly grounded) will probably provide sufficient protection during normal operation. I've also observed that electronic devices mounted in the panel front are vulnerable also. These are generally display rather than control. Darold Woodward PE SEL Inc. [email protected]
Hello List, Our customers also complained once that touch screens use to get activated by the interference of the Walkie Talkie. BR /Girish
Anyone believing that because it hasn't happened thus far, it won't happen at all, is making a serious error. I recall several mAjor catastrophes (by anyone's definition) caused by Radio Frequency Interference (RFI). Both AM and FM type transceivers were involved. The now defunct organization, SAMA, issued a test standard intended to measure immunity to RFI interference. It includes a table comprised of two parameters: proximity of the hand-held radio (RFI generator) to the subject device; and the radio's maximum field-strength. In some cases energy is added to analog measuring circuits resulting in a higher than desired signal. In other cases it only has to cause a one-bit change during program execution. I don't remember, nor do I have access to the pertinent Standard Number. However, someone mentioned it in an earlier posting as being available thru Global Documents. Regards, Phil Corso, PE Trip-A-Larm Corp (Deerfield Beach, FL)
This might sound interesting close to what you have experienced.

We were commissioning a steel plant and we observed that the the electronics of DC Dives (Ananlog) was going haywire at times.

No wonder it took us more than a couple of days to find that we had the main DC drive control panel in the next room. These two rooms were separated by just a wooden partition. The field current of this motor was as hight as 400A. This definitely caused an induction in the panels around 4 meters away.

No prize for guessing that we had to shield the room as well as bring the field current down by replacing the DC motors. And that was a happy end to a sad story.

If you are facing similar problems with RF signals, it does not surprise me although here the difference is we are talking about digital systems and RF signals. In my opinion, poor EMI protection in design of the CPU module can cause such problems (Only the OEM can help with data). Doing proper earthing should help.
Keying a walkie-talkie switch produces an electromagnetic impulse, that is like a bolt of lightening, but on a much reduced power level. An "impulse" has an almost infinite frequency response which means it produces energy at almost every frequency and can get into just about any frequency tuned device if it is strong enough.
It will easily get into millivolt type signals (T/Cs, internal memory voltages,etc.). I wouldn't be surprised to find that cell phones can do the same thing in the right circumstances.
Two tin cans and a taught string, however, show no evidence of disrupting a PLC or other control devices.

Timothy P Niemczyk

Regarding Walkie talkie near PLC issues, tests attempting to reproduce source, path, and consequence in a root-cause determination have failed to demonstrate or reproduce the root cause. This failure to determine the failure is because the conditions of the test may not have reproduced the original event with sufficient accuracy. Most reports attribute the event to EMI/RFI because there was a source that was close to the component during the event. In other report, specific EMI/RFI source is not disclosed resulting in the statement that the event "May" have been caused by a spurious signal or voltage spike. If the system is engineered without EMI/RFI design considerations, then the number of potential noise sources and paths exceeds any practical evaluation of the root cause. Therefore, engineers must consider products that are tested against Military or Industry Standards, i.e. MIL-STD-461E or IEC 61000 <pre>
Test Methods MIL-STD-461E
CS114 Conducted susceptibility, bulk cable injection, 10 kHz to 200 MHz
CS115 Conducted susceptibility, bulk cable injection, impulse excitation
CS116 Conducted susceptibility, damped sinusoidal transients, cables and power leads,
10 kHz to 100 MHz

Test Methods IEC 61000
IEC 61000-4-1, Overview of Immunity Tests, European Committee for Electrotechnical
Standardization, 1995.
IEC 61000-4-4, Electrical Fast Transient/Burst Immunity Test, European Committee for Electrotechnical Standardization, 1995.
IEC 61000-4-5, Surge Immunity Test, European Committee for Electrotechnical Standardization,
IEC 61000-4-6, Immunity to Conducted Disturbances, Induced by Radio-Frequency Fields,
European Committee for Electrotechnical Standardization, 1996.</pre>