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regarding basic doubts

D

dhana

Jan 1, 1970
0
I have messages which has to be cleared

1. whether A.C voltage is effective or D.C voltage is effective. what
is the D. C equivalent A. C voltage

2. when current is passed into human body what is minimum d.c and a.c
voltages

3. when telephone is ringing what is the a.c voltage and d.c voltage
are produced. and explain how
 
dhana said:
I have messages which has to be cleared

1. whether A.C voltage is effective or D.C voltage is effective. what
is the D. C equivalent A. C voltage

2. when current is passed into human body what is minimum d.c and a.c
voltages

3. when telephone is ringing what is the a.c voltage and d.c voltage
are produced. and explain how

This is a dumb newby question, which ought to have been posted on
sci.electronics.basics.

1. alternating current and direct current can both be effective in many
applications. In some you need to use one or the other. When it comes
to heating up a resistive load, the heating effect of the sinusodal
alternating current has to be integrated over one full cycle of the
sine wave, and people talk about the root means square voltage averaged
over the full cycle, which turns out to be 2/pi of the peak voltage.

The "230V" 50Hz main voltage has the same heating effect on a resistor
as a 230V DC voltage, but the alternating current cycles between peak
values of +361V and -361V.

2. 50Hz AC is much more effective at damaging human beings than direct
current.

Voltages less than 24V - in the range +24V to -24V - are legally
accepted as not dangerous.

3. Telephone ring tone is an interrrupted direct voltage, nominally
50V, though it can be quite a lot lower at the end of a long connection
to the local exchange.

It used to be produced by 48V stacks of lead acid batteries. I don't
know what is typically used today.
 
P

Phil Allison

Jan 1, 1970
0
1. alternating current and direct current can both be effective in many
applications. In some you need to use one or the other. When it comes
to heating up a resistive load, the heating effect of the sinusodal
alternating current has to be integrated over one full cycle of the
sine wave, and people talk about the root means square voltage averaged
over the full cycle, which turns out to be 2/pi of the peak voltage.


** Huh ??

Care to think that one over - Bill ???

The "230V" 50Hz main voltage has the same heating effect on a resistor
as a 230V DC voltage, but the alternating current cycles between peak
values of +361V and -361V.


** At least it is consistently wrong.

The ratio of peak to rms for a sine wave is 0.7071 or 1/ sq rt 2

The ratio of peak to *average rectified value* is 2/pi.




........ Phil
 
Phil said:
** Huh ??

Care to think that one over - Bill ???




** At least it is consistently wrong.

The ratio of peak to rms for a sine wave is 0.7071 or 1/ sq rt 2

The ratio of peak to *average rectified value* is 2/pi.

Thanks Phil. Another senior moment ...
 
F

feebo

Jan 1, 1970
0
3. Telephone ring tone is an interrrupted direct voltage, nominally
50V, though it can be quite a lot lower at the end of a long connection
to the local exchange.

It used to be produced by 48V stacks of lead acid batteries. I don't
know what is typically used today.

ayup Bill...

Not quite right here - telephone line voltage is generally -50VDC -
the ring voltage is usually 70-100 VAC

The line voltage drops to about 11V when the receiver is lifted, this
is down to the voltage drop of the telephone circuit and the "relay
coil" in the exchange (used to be a relay but now simulated for
compatibility by the electronics)
 
F

feebo

Jan 1, 1970
0
I have messages which has to be cleared

1. whether A.C voltage is effective or D.C voltage is effective. what
is the D. C equivalent A. C voltage

2. when current is passed into human body what is minimum d.c and a.c
voltages

3. when telephone is ringing what is the a.c voltage and d.c voltage
are produced. and explain how

1. DC voltage generally does more "work" than the same AC voltage -
this is because the AC voltage is constantly changing polarity and so
can't spend all it's time at peak. The equivalent voltage for AC to do
the same work as DC is called "Root Mean Squared" - you may have seen
RMS referred to a lot. When a voltmeter measures AC, it will most
likely give you RMS, but because the voltage is changing, it has to
peak much higher than this to cover up for the short falls in the
times when it is doing very little work. Consequently if you look with
an oscilloscope at 240V line voltage, you see that it actually peaks
at about 340V.
I can't remember the equation for RMS (google it), but if you remember
the magic number 0.7071, this is the ratio of DC to AC for equivalent
work done, so 1:0.7071 will give the work done by the same peak AC.
240v / 0.7071 gives 339V - so the RMS is calculated by multiplying the
peak by the ratio above.

2. the question doesn't give enough info... what are you expecting the
human body to do? Are you looking for typical resistance of body
tissues (and thus current at specific voltages?)

3. A telephone line has about 50VDC sat on it all the time. When a
ringing signal is passed to it, the 50VDC is momentarily replaced with
70-100VAC - the 50V you won't feel across your fingers but ring signal
stings a bit. The AC signal used to be generated from a cam on a motor
rotating at a set speed. If the cam has two bumps (UK BRRRR BRRRR ring
as opposed to US BRRRRRRRRRRR) on it, as it rotates, the bumps cause a
set of contacts to close and the 70VAC signal is fed to the line.
Often there were several cams to reduce the current requirements on
the ring generator - these would be out of phase with each other so as
to share the load. Modern exchanges generate the ring tone
electronically and do not use a motor with cams anymore.
 
J

Jim Thompson

Jan 1, 1970
0
1. DC voltage generally does more "work" than the same AC voltage -
this is because the AC voltage is constantly changing polarity and so
can't spend all it's time at peak. The equivalent voltage for AC to do
the same work as DC is called "Root Mean Squared" - you may have seen
RMS referred to a lot. When a voltmeter measures AC, it will most
likely give you RMS, but because the voltage is changing, it has to
peak much higher than this to cover up for the short falls in the
times when it is doing very little work. Consequently if you look with
an oscilloscope at 240V line voltage, you see that it actually peaks
at about 340V.
I can't remember the equation for RMS (google it), but if you remember
the magic number 0.7071, this is the ratio of DC to AC for equivalent
work done, so 1:0.7071 will give the work done by the same peak AC.
240v / 0.7071 gives 339V - so the RMS is calculated by multiplying the
peak by the ratio above.

2. the question doesn't give enough info... what are you expecting the
human body to do? Are you looking for typical resistance of body
tissues (and thus current at specific voltages?)

3. A telephone line has about 50VDC sat on it all the time. When a
ringing signal is passed to it, the 50VDC is momentarily replaced with
70-100VAC - the 50V you won't feel across your fingers but ring signal
stings a bit. The AC signal used to be generated from a cam on a motor
rotating at a set speed. If the cam has two bumps (UK BRRRR BRRRR ring
as opposed to US BRRRRRRRRRRR) on it, as it rotates, the bumps cause a
set of contacts to close and the 70VAC signal is fed to the line.
Often there were several cams to reduce the current requirements on
the ring generator - these would be out of phase with each other so as
to share the load. Modern exchanges generate the ring tone
electronically and do not use a motor with cams anymore.

Just hold onto the wires and have someone "ring you up" ?:)

...Jim Thompson
 
P

PeteS

Jan 1, 1970
0
Jim said:
Just hold onto the wires and have someone "ring you up" ?:)

...Jim Thompson

That gives a whole new meaning to 'Please hold the line'

;)

Cheers

PeteS
 
M

Michael A. Terrell

Jan 1, 1970
0
PeteS said:
That gives a whole new meaning to 'Please hold the line'


Or:

"Start me up"!
"Come on, Baby, light my fire"!
"Ring of fire"! (cue Johhny Cash)
"I saw the light"! (cue Hank Williams)
"Great balls of fire"! (cue Jerry Lee Lewis)

;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
H

Homer J Simpson

Jan 1, 1970
0
Just hold onto the wires and have someone "ring you up" ?:)

Or piss off the Chicago cops and they'll do it to you.
 
J

Jon Elson

Jan 1, 1970
0
feebo said:
3. A telephone line has about 50VDC sat on it all the time. When a
ringing signal is passed to it, the 50VDC is momentarily replaced with
70-100VAC - the 50V you won't feel across your fingers but ring signal
stings a bit. The AC signal used to be generated from a cam on a motor
rotating at a set speed. If the cam has two bumps (UK BRRRR BRRRR ring
as opposed to US BRRRRRRRRRRR) on it, as it rotates, the bumps cause a
set of contacts to close and the 70VAC signal is fed to the line.
Often there were several cams to reduce the current requirements on
the ring generator - these would be out of phase with each other so as
to share the load. Modern exchanges generate the ring tone
electronically and do not use a motor with cams anymore.
I got a tour of the #5 ESS installation in our local phone exchange (I'm
pretty
sure they are STILL running this system) and they had an ANCIENT looking,
like 1930's rotary converter with cam-operated switches to generate the
90 V 20 Hz ring signal, as well as the 600 + 1000 Hz dial tone signal.
I was astonished that they were using such an antique, but it apparently was
the accepted way to do it. It had oil cups that had to be filled every
couple
of days to keep the Babbit bearings from burning up. I think it had a
centrifugal
governor roughly of the fly-ball sort that switched contacts on the DC motor
field circuit. It ran from the 48 V main system batteries, just like
everything
else, including some of the building lights. They had a Solar gas turbine
generator set on the roof for extended power outages.

Jon
 
R

Rich Grise, Plainclothes Hippie

Jan 1, 1970
0
Or:

"Start me up"!
"Come on, Baby, light my fire"!
"Ring of fire"! (cue Johhny Cash)

I thought this was the one they used in the commercial for hemmorhoid
cream. ;-P


Cheers!
Rich
 
F

feebo

Jan 1, 1970
0
I got a tour of the #5 ESS installation in our local phone exchange (I'm
pretty
sure they are STILL running this system) and they had an ANCIENT looking,
like 1930's rotary converter with cam-operated switches to generate the
90 V 20 Hz ring signal, as well as the 600 + 1000 Hz dial tone signal.
I was astonished that they were using such an antique, but it apparently was
the accepted way to do it. It had oil cups that had to be filled every
couple
of days to keep the Babbit bearings from burning up. I think it had a
centrifugal
governor roughly of the fly-ball sort that switched contacts on the DC motor
field circuit. It ran from the 48 V main system batteries, just like
everything
else, including some of the building lights. They had a Solar gas turbine
generator set on the roof for extended power outages.

Jon

you are absolutely right Jon. I was in Skyport Exchange (at Heathrow)
a couple of months ago and while they don't actually uses this
generator in daily use, they still have two as standby. They are both
kept running (as they have done for years & years). the reason behind
the thinking is that in times of national uproar (worst case scenario
a nuking - remember this stuff has been there since the 50's when it
all looked like it was gonna go off with the USSR) a motor and
contacts will not be affected by EMP. If they pull the preference
jumpers (and the phone system becomes specific to government and the
emergency services) they can resort ot an electrical system based
around relays and stuff which is rad-hard.
 
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