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How to block 60 Hz siginal to scope.

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mech11
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Joined: January 3rd, 2018, 9:42 pm
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How to block 60 Hz siginal to scope.

Post by mech11 » January 3rd, 2018, 9:48 pm

I have a medical office call box/light system that is older probably 20 year old and they moved the main panel that the Drs see to know when there are patients waiting and since they moved it, it is intermittently not working. The system uses a siginal that is transmitted over the AC connection/plug.
I am new to oscilloscopes but purchased one to see if I could observe if the siginal is too weak in the new location (it’s about 250 feet from where it was originally) or if it’s getting too much interference.
I have found that the system needs to be on its own circuit and have a 2700 UH choke installed on the circuit feed but that’s about all I can come up with since apparently the manufacture has gone out of business. They do still have a website but only very limited information and no schematics.
http://www.varitronics.com/ts-cs2install-nc.htm
My problem seems to be when I look at the pattern all I can identify is the 60hz siginal and don’t see any changes when energizing one of the boxes and would like to know if anyone has any suggestions for blocking out the 120V 60Hz siginal so I can see the siginal that is used to operate these boxes over the 120V line. I believe I need a high pass filter but not sure what components I would need to achieve blocking the unwanted siginal but still be able to pass the triggering siginal that the boxes use to communicate to each other.
Thanks in advance for any help you may be able to provide.

w2aew
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Re: How to block 60 Hz siginal to scope.

Post by w2aew » January 4th, 2018, 8:26 am

While I don't know anything specific about this system and what it's signals look like, it appears that the 2700uF inductors are intended to isolate the main power panel from the control system by raising the impedance seen looking from the control units to the panel, at the operating frequency. This is also the reason why they instruct to not to common the neutral (whites). However, there doesn't appear to be any information about the operating frequency of the signaling system, so we don't know how far above 60Hz the signals are located. This makes it difficult to design an appropriate filter.

Let's assume that it operates in the 10s of kHz or higher. You certainly can start off with something like a 0.01uF (10nF) capacitor from the hot lead to a 10K resistor to Neutral, then put your scope across the 10Kohm resistor. I am assuming that you're using a battery powered scope, or at least a scope with isolated (non-grounded) inputs. And of course, use extreme caution when working with line voltages.

tuvela
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Re: How to block 60 Hz siginal to scope.

Post by tuvela » June 12th, 2018, 8:43 am

If the call box moved to a different outlet, this can cause problems. - the wiring through the breaker box. Say before the call box and the receiving boxes were on the same breaker and communication worked.

Now move the call box to another breaker. There is more stuff between it and the receiving boxes now. Even worse, move the call box to the other 110V circuits (the other side of the power pole transformer. Now signals have to run out to the electric utility transformer, back into the building and through a bunch of wire to the receivers.

Think about this, trace some circuits and see if that helps any.

Steve

Kiriakos
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Re: How to block 60 Hz siginal to scope.

Post by Kiriakos » September 1st, 2018, 12:12 pm

mech11 wrote:
January 3rd, 2018, 9:48 pm
I have a medical office call box/light system that is older probably 20 year old ...... The system uses a signal that is transmitted over the AC connection/plug.

I am new to oscilloscopes but purchased one to see if I could observe if the signal is too weak in the new location.
Any system uses a signal that is transmitted over the AC connection/plug, it does that in another frequency than 50 or 60 Hz.
Now because 120V 60Hz is the signal with highest amplitude, any oscilloscope by the use of Auto-set will trigger over this signal.

Similar application this is using single phase (power line ) wires as wires for communications, this is power-line wall mount devices for Ethernet connection and internet sharing among computers in the same house.

Derrils
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Joined: September 19th, 2018, 2:36 am
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Re: How to block 60 Hz siginal to scope.

Post by Derrils » September 19th, 2018, 2:43 am

I am using a PCI-6110 and noticed that if I connect a o-scope up to one of the analog inputs I can see a roughly sinusoidal 60hz >100mV signal on the scope screen. Once my application exits, however, the signal stops.

In my app, I am setting up the 4 analog channels to use an external 5Mhz sample clock and an external gate signal. These two signals are generated by another board and piped-in over the RTSI bus. Because the sample clock can not be pulled from the RTSI on this card, I send it out to the connector block, jump it to the proper PFI on the block, and then it is send back to the card. As you may expect, this signal appears to couple to the Analog Input a bit, but only as long as I leave the scan clock running. The signal I am trying to hunt down now is only present once I turn the clocks off.

When finished acquiring data, my app uses the AIClear VI to reset the Analog portion of the card, and uses the Counter Stop VI and Counter Control VI to stop the counters. After calling these VI's is when I see the signal in question.

I should also mention that I am using a BNC-2110 connecting block vacuum, and that the ground source switch is set to FS. If I switch it to GS, the signal on the scope gets MUCH larger and is a much cleaner sine wave.

Does anyone have any ideas what may be the cause of this signal and how I can get rid of it???

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