60 Cycle Interference

[fozzy40]

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I'm using a Cadwell Sierra Wave and having a hard time getting rid of 60 cycle interference. I've tried all of the basic stuff and still having a hard time getting a good baseline.

Every machine is quirky but would you guys please share some of your tricks?

Draping the wires on the patient while needling used to work well on my last machine.

 

[Taus]

That's one of the main machines I've trained on....love it... especially the automatic full sentence write-up of the nerve conduction data. I recall a setting that some attendings had as automatic and some had to be turn on- one of the filters had an icon to click on or off at the top left of the screen.

Perhaps the office/room/building you're in?

 

[fozzy40]

I'm sure there is something to the building but unfortunately it falls under my "uncontrollable factor' category. The only thing I can really control is to not do the study near a window...haha!

 

[PMR2008]

I have used a Cadwell Sierra Wave.
1) Did you turn on the notch filter? It helps but does not eliminate 60 cycle.
2) Did you check the wiring in the room? Maybe you could try to move to a different room. Also unplugging unnecessary wires could work. Removing any transformers and moving away from large wires carrying AC current is imperative.
3) If your table has any attached wires it could be the culprit. If it is a metal table you can try grounding it.
4) Florescent lights are notorious for causing 60 cycle while incandescence lights work better.
5) Make sure it is not the electrodes themselves.

If all else fails maybe this might work.
http://www.autom8.com/hum_bug.html

 

[Taus]

notch filter! thanks pmr08.... that's what I was getting at

 

[Jumpu]

I have noticed the same issue with our cadwells. I think I'll try changing the filters when I get back to work.

 

[fozzy40]

Have you actually seen/tried the hum bug?

 

[PMR2008]

Have you actually seen/tried the hum bug?

Nope. Apparently it works by subtraction but I wonder if it will affect the amplitude of waveforms.

"The Hum Bug can eliminate 50/60 Hz noise from virtually any analogue signal. It is equally effective at removing noise associated with inadequate grounding, ground loops, and electrical pickup. Common applications include noise elimination from signals recorded using microelectrodes, skin electrodes (EKG, EMG, EEG), high gain amplifiers, magnetic sensors, and audio equipment"

Maybe will give it a shot once I start practicing and if I have major 60 cycle issues (it costs 1700 bucks). Also I am not sure if the Cadwell has the appropriate input/output for the humbug.

 

[PMR 4 MSK]

The closer my wires are to the pt, the more interference I get. Also dangling wires.

Skin - skin contact helps.

You can get a shielded electric outlet.

Are you getting 60 cycle more with NCS or EMG?

 

[fozzy40]

The closer my wires are to the pt, the more interference I get. Also dangling wires.

Skin - skin contact helps.

You can get a shielded electric outlet.

Are you getting 60 cycle more with NCS or EMG?

During EMG. I'll try to keep the wires away and see if that helps. On my old machine, the more I draped the wires on the on the patient the better. Go figure!

What is a shielded electric outlet?

 

[RUOkie]

I get that intermittently with my SierraWave. Usually it means I have a bad electrode, or need to move my amplifier (I have a habit of keeping it on the exam table).

The last time I had bad 60hz noise, it was because my base unit's ground had become dislodged from the computer.

When you are getting 60hz noise, it means you have interference from your environment. Check ALL your connections, change electrodes, and you will fix the problem. If all else fails, get your room rewired with a dedicated circuit that is sheilded. (it does not cost much if you have a good electrician). No need to get a shielded room like the old days.

 

[jmaguire]

I'm being killed with 60 cycle interference, and have tried every big change I can make. I'm in a single exam room office, and can't move the Wave to another room. I put in a dedicated Hospital ground outlet today, and still am getting interference. Changed the pre-amp, checked all the connections and am stuck. Getting real difficulties with sensory NCS's and EMG having to average alot (and killing the patients).

Last shot I can think of is to buy shielded wires (clips for disponsable pickups)...has anybody found these help? Already spent a silly amount putting in the dedicated outlet...so I'm willing to go for the extra $100 for the shielded but would love some input.

For context: used a Wedge for nearly 9 years without problems. Used to belong to a large practice and had a great flat baseline on EMG and NCS. Now in new practice and got a Wave. The best "flat baseline" i've gotten is some continuous serrated interference up to 20-30 uV on EMG active monitor. Feel like getting environmental interference but I can't seem to improve any more than I have. Sucks because I feel like I could be missing out on some of the smaller amplitude responses on NCS. Is the Wave more sensitive than the Wedge?

ANY advice would be great...

 

[RUOkie]

I'm being killed with 60 cycle interference, and have tried every big change I can make. I'm in a single exam room office, and can't move the Wave to another room. I put in a dedicated Hospital ground outlet today, and still am getting interference. Changed the pre-amp, checked all the connections and am stuck. Getting real difficulties with sensory NCS's and EMG having to average alot (and killing the patients).

Last shot I can think of is to buy shielded wires (clips for disponsable pickups)...has anybody found these help? Already spent a silly amount putting in the dedicated outlet...so I'm willing to go for the extra $100 for the shielded but would love some input.

For context: used a Wedge for nearly 9 years without problems. Used to belong to a large practice and had a great flat baseline on EMG and NCS. Now in new practice and got a Wave. The best "flat baseline" i've gotten is some continuous serrated interference up to 20-30 uV on EMG active monitor. Feel like getting environmental interference but I can't seem to improve any more than I have. Sucks because I feel like I could be missing out on some of the smaller amplitude responses on NCS. Is the Wave more sensitive than the Wedge?

ANY advice would be great...

Is the machine new? I did burn through an amp after 6 yrs of use. I called CADWELL and they talked me through some diagnostics on the machine, and then overnighted me a new amplifier and I sent my old one back. They fixed the old amp for $750 (including the new one)

The sheilded cables help a little.

 

[PMR 4 MSK]

Call Caldwell and ask for the hardware dept. they can have you check a few things over the phone. They will likely want you to send the unit in, and can send you a rental n the meantime.

Alternatively, ask a rep to come check it out.

 

[jmaguire]

I''m going to try some shielded cable, but my working theory is that the room must have some serious electrical wiring around it (HVAC, etc) that I can't see.

At this point I may have to rely more on the speaker than the scope.

 

[JonDO]

I battled with this issue when I moved to a new office. I started to unplug every equipment in the room one-by-one, until I figured out it was the hand control module for the exam table. Now, I just move the control away from the body part being tested, and voila! Turning on the notch filter helps tremendoulsy too.