9448 Scantronic

[Fred555]

I can see none of you are going to get the theory behind one hand in pocket when using a multimeter - it is very simple - lean (dead casual like) with left hand on earthed conductive (metal) surface, now make a slip with the other hand that is holding a test lead and what path does the electricity take?

Across the chest - through the heart (a pump that is controlled by muscles that are controlled by electrical impulse) and that will generate a generally fatal arrhythmia which stops the heart and you are then dead - permanently.

Think about it - the next time an overdramatic medical drama is on TV when the doctors want to defibrillate a patient to restart the heart the shock paddles go on the chest on either side so the jolt travels through the heart - they do not connect to toes or ears or any other protrusions because the current will not travel across the heart so you will not restart it. But low resistance is important to get the current to travel well so the shock paddles use some conductive jelly (also stops skin burns).

So by keeping one hand in the pocket you will not be able to lean (without thinking) and make good sweaty palm to earthed metal surface contact and if your other hand slips with the test probe the shock will travel to your feet and your shoes will act as some insulation reducing the shock (as there is a lower total electrical potential - the reason 110V site transformers exist is that they limit your shock potential to 55 volts - seldom fatal as the voltage is low enough that resistance becomes an issue) but most importantly of all the jolt will not go across your heart and kill you.

PS Portable Defibrillators use a mere 12 Volt battery to generate that shock that restarts a heart and when the medics yell "Charge 320 - Clear" on TV they are referring to mA shock value they are going to give the patient - control panels have at least 1000mA at 12VDC on tap.

I have noted that your guides to alarm servicing include working on an opened, live, mains powered, non isolated, control panel - any member of the public asking for and taking advice in these forums should remember caveat emptor - let the buyer beware.

My advice is merely my opinion it is not right, it is not wrong, it is just an opinion - it is what I would do before I even bothered to fit a new battery but if somebody is poking around looking for advice and information but has not got a clue what they are doing then they should not take the advice - they should instead pay somebody who does know what they are doing and not be so tight-fisted - there is nothing worse than someone who constantly demands advice, never takes it or uses it and is back next week whinging, moaning and bitching about the same thing - they are just leaches who are trying to nag someone into giving them a freebie.

Rant Over!! No disrespect whatsoever intended to anyone and FYI Piercings and Amalgam Tooth Fillings heat up dramatically with electrocution! Good one lawandorder!

[lawandorder]

I can see none of you are going to get the theory behind one hand in pocket when using a multimeter - it is very simple - lean (dead casual like) with left hand on earthed conductive (metal) surface, now make a slip with the other hand that is holding a test lead and what path does the electricity take?

Across the chest - through the heart (a pump that is controlled by muscles that are controlled by electrical impulse) and that will generate a generally fatal arrhythmia which stops the heart and you are then dead - permanently.

Think about it - the next time an overdramatic medical drama is on TV when the doctors want to defibrillate a patient to restart the heart the shock paddles go on the chest on either side so the jolt travels through the heart - they do not connect to toes or ears or any other protrusions because the current will not travel across the heart so you will not restart it. But low resistance is important to get the current to travel well so the shock paddles use some conductive jelly (also stops skin burns).

So by keeping one hand in the pocket you will not be able to lean (without thinking) and make good sweaty palm to earthed metal surface contact and if your other hand slips with the test probe the shock will travel to your feet and your shoes will act as some insulation reducing the shock (as there is a lower total electrical potential - the reason 110V site transformers exist is that they limit your shock potential to 55 volts - seldom fatal as the voltage is low enough that resistance becomes an issue) but most importantly of all the jolt will not go across your heart and kill you.

PS Portable Defibrillators use a mere 12 Volt battery to generate that shock that restarts a heart and when the medics yell "Charge 320 - Clear" on TV they are referring to mA shock value they are going to give the patient - control panels have at least 1000mA at 12VDC on tap.

I have noted that your guides to alarm servicing include working on an opened, live, mains powered, non isolated, control panel - any member of the public asking for and taking advice in these forums should remember caveat emptor - let the buyer beware.

My advice is merely my opinion it is not right, it is not wrong, it is just an opinion - it is what I would do before I even bothered to fit a new battery but if somebody is poking around looking for advice and information but has not got a clue what they are doing then they should not take the advice - they should instead pay somebody who does know what they are doing and not be so tight-fisted - there is nothing worse than someone who constantly demands advice, never takes it or uses it and is back next week whinging, moaning and bitching about the same thing - they are just leaches who are trying to nag someone into giving them a freebie.

Rant Over!! No disrespect whatsoever intended to anyone and FYI Piercings and Amalgam Tooth Fillings heat up dramatically with electrocution! Good one lawandorder!

I think most engineers fully understand the theory behind using only one hand when working on potentially live equipment, most electricians, particuarly commercial ones instinctively lean away from the current source when working on large control panels and distribution boards so if they collapse for any reason they tend to fall away from the source rather than in to it.

TV engineers (when they existed) used to do the same and yes one hand well away from any earth path is a wise precaution.

The measurement used when defribilating patients is not milliamps it is joules and although the battery voltage in some de-fibs is only 12 volts the voltage is raised significantly before being discharged into the patient (or victim depending on outcome). 12 volts even across the chest would not have any effect whatsoever aprt from perhaps a mild tingling.

[Fred555]

lawandorder - I am pleased to see you understand the theory as well as practice - as some people do a very good impersonation of someone who understands/knows no theory whatsoever.

I stand corrected on mA but how would you go about converting from Joules into mA ?

And any idea what the Defibrillator shock voltage would be?

I sincerely hope the pulse transformer in the Defib. is not a disguised car ignition coil! Patient could then definitely be a victim!

[lawandorder]

lawandorder - I am pleased to see you understand the theory as well as practice - as some people do a very good impersonation of someone who understands/knows no theory whatsoever.

I stand corrected on mA but how would you go about converting from Joules into mA ?

And any idea what the Defibrillator shock voltage would be?

I sincerely hope the pulse transformer in the Defib. is not a disguised car ignition coil! Patient could then definitely be a victim!

A Joule is a measurement of energy so time becomes a factor, 1 joule is equivalent to 1 amp flowing for 1 second being driven by 1 volt.

Most external defibrillators shock at a voltage between about 250 and 450 volts DC. The characteristic whistling noise they make is the inverter which charges the high voltage capacitor, pretty much the same as the inverter in an intruder alarm strobe light or camera flash.

[Guest RJBsec]

All very arfuresque!

[hpotter]

All very arfuresque!

Well, it made my heart stop.

[Fred555]

A little suspicious (don't you think) the voltages being so similar to single phase and three phase electricity supply in the UK?

What goes on in NHS these days - car jump leads from a convenient mains socket to patient?

Also the same as in a Capacitorized Discharge Ignition System - the spark duration is so short the HT leads can be wet and the car still starts and runs perfectly - I told you it is all starting to look like an ignition coil in disguise I just did not realise it was a CDI coil - how brutal - poor patient - CDI is only used on high compression/power engines.

Anybody feel like actually doing the maths to convert from Joules to mA.

[lawandorder]

A little suspicious (don't you think) the voltages being so similar to single phase and three phase electricity supply in the UK?

What goes on in NHS these days - car jump leads from a convenient mains socket to patient?

Also the same as in a Capacitorized Discharge Ignition System - the spark duration is so short the HT leads can be wet and the car still starts and runs perfectly - I told you it is all starting to look like an ignition coil in disguise I just did not realise it was a CDI coil - how brutal - poor patient - CDI is only used on high compression/power engines.

Anybody feel like actually doing the maths to convert from Joules to mA.

You can't convert joules to ma, the two terms measure different things. One is current the other is energy.

It's like you can't convert watts to volts because they are measures of different entities.

As you say, it is highly suspiscious that they use standard voltages but personnaly I have no objection to them using jump leads as long as they don't start anything.