hello people...

i have attached a circuit that acts as an amplifier for biological signals... E1, E2 and E3 are the electrodes that will pick up the signals from the human body... these signals are amplified and filtered...

As u can see electrode E3 is the reference electrode or the ground electrode... i have a problem here.... the op-amps used must be provided with a +/-12V dc supply...

where must the ground of the power supply be connected to? i cannot connect it to the same ground as E3 (the reference electrode) as the user ight experience shock...

i need to isolate these two grounds, otherwise the circuit wont work... can u pls help me?

Attached Images

bio_proj.JPG (32.3 KB, 13 views)

 

Welcome to the forums, oh wait you've been here three years and you started a thread with "help me pls..."

PS please stop using sms speak.

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am sorry.... :-)

i was not quickly getting wat to give as the title.. so had to give that.... anyway i hope the new title makes more sense...

 

hello people...

i have attached a circuit that acts as an amplifier for biological signals... E1, E2 and E3 are the electrodes that will pick up the signals from the human body... these signals are amplified and filtered...

As u can see electrode E3 is the reference electrode or the ground electrode... i have a problem here.... the op-amps used must be provided with a +/-12V dc supply...

where must the ground of the power supply be connected to? i cannot connect it to the same ground as E3 (the reference electrode) as the user ight experience shock...

i need to isolate these two grounds, otherwise the circuit wont work... can u pls help me?

Attached Images

bio_proj.JPG (32.3 KB, 3 views)

 

The user shouldn't experiance a shock because the op-amp inputs have a very high impedance and the current flowing would be far to low to shock.

You can build a +/-12V supply from a 9V transformer, a couple of diodes and a capacitor. Of course it won't be regulated but op-amps don't need a regulated supply.

Attached Images

+- 12V Supply.GIF (2.6 KB, 11 views)

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thank u for the circuit....

i already have a dc power supply that gives me +/-12V dc... now that DC power supply box has a ground pin that we connected to the ground that i have shown in the diagram....

in that case i sensed a minor pain in the place where i connected these electrodes.... (luckily a minor... :-).... later on i read about isolating these grounds.....

how can i achieve this?

 

Are you just measuring AC signals?

I'm surprised it shocked you. I suppose 24V on moist skin it liks a 9V battery on the tongue.

You could just add 100nF capacitors to two of the inputs.

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Duplicate post.

http://www.electro-tech-online.com/e...lp-me-pls.html

Please don't ask the same question more than once.

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Generally such equipment should have the body connected to perfect earth-- not to leave it to Ground earth of the Public mains. In some countries, there is no standardisation like third pin earth.
Hence we have 2 pin sockets at mains. Obviously, in such cases the adopter or wall wart what some people call it, is likely to give a small shock when the electrodes of the equipment are connected to the body.
Mr Raviram should first try the device from battery only in order not to get electrocuted even to a minor extent.

Designing power supplies for medical applications, must exclusively be different even at component level and the requisite standards followed. A three pin (after ensuring that the wiring has an earth provided and it is effective.)

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Wall warts have a built-in isolation transformer that provides a protective barrier from the mains.

Mains powered equipment is normally powered from a 1:1 isolation transformer anyway. This is because RCDs are not a good idea as they cut the power and endanger life.

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The so called adopters / battery eliminators also have a step down isolation transformer(with windings one over the other- not the two bobbin type). But due to cheap manufacture they are not fit for medical equipment use.

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I don't know about the kinds of mains adaptor found in your country but the ones here in the UK are all double insulated.

Always check that it has the following symbol, "Class two", "double insulated" or similar written on it.

Attached Images

Double insulated symbol.GIF (1.1 KB, 27 views)

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I got your point Hero999.

The transformers meant for scientific or engineering level would afford separate bobbins for primary and secondary.

Little cheaper ones use same bobbin but provide a non-shorted copper foil as a shield between Pri and Sec, in addition to two layers of insulation tape. the copper foil is electrically connected to the 3rd pin we call ground. These transformers have a copper shield outside also.

Next version has only 2 layers insulation tape while the winding is is on one bobbin.

But the commercial ones for entertainment electronics follow the last category. Even some times the minimum honour of 10 turns per volt standard is not followed, leave alone the gauge of wire used. So the problems arise due to possible low insulation and non grounding of the transformer body

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Sarma.

 

i came across this circuit which i have attached below....

the description goes like this...
Before hooking up electrodes to the user, build the precautionary safety circuit... the source refers to the user who is going to put o the electrodes...

will this serve my purpose?? i have also heard about opto-isolators....

Attached Images

isolation_circuit.JPG (18.2 KB, 5 views)