J
James Lerch
- Jan 1, 1970
- 0
So,
A friend and I are having a polite debate.
He's calculating the current in a circuit my measuring the voltage
drop across a 20ohm resistor. (Current is ~30mA range for refernce)
I think best approach is to put a mA meter in series with circuit and
read the meter. He disagrees and said his method of measuring the
voltage drop across the resistor is more accurate.
His claim is the mA meter adds resistance to the circuit and under
reports the results. I agree in theory with his statement, but
disagree on the magnitude of the error.
I claim the amount of error in both the ability to measure 0.6vdc and
the error in the certaitnty of his "known" resistance is of a larger
concern.
For the record, were just simple tinkerers, using simple (but not
junk) tools, working remotetly from each other. No one's life or
livelyhood depend on the results.
If a little background will help, here's the circuit.
5vdc -> led -> resistor -> led -> pin on shift register -> gnd
Leds drop ~2v each (rated at max of 30mA current)
Resistor is 1/4 watt carbon film 20ohm +/- 5% variety
Shift register on resistance is rated at 6.5ohm at 50ma at temp of 25c
I agree with him that he should use a 33ohm resistor for safety sake,
but would like debate resolution over using a mA meter
So, what's the collective opinion on this?
--
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)
"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"
" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
A friend and I are having a polite debate.
He's calculating the current in a circuit my measuring the voltage
drop across a 20ohm resistor. (Current is ~30mA range for refernce)
I think best approach is to put a mA meter in series with circuit and
read the meter. He disagrees and said his method of measuring the
voltage drop across the resistor is more accurate.
His claim is the mA meter adds resistance to the circuit and under
reports the results. I agree in theory with his statement, but
disagree on the magnitude of the error.
I claim the amount of error in both the ability to measure 0.6vdc and
the error in the certaitnty of his "known" resistance is of a larger
concern.
For the record, were just simple tinkerers, using simple (but not
junk) tools, working remotetly from each other. No one's life or
livelyhood depend on the results.
If a little background will help, here's the circuit.
5vdc -> led -> resistor -> led -> pin on shift register -> gnd
Leds drop ~2v each (rated at max of 30mA current)
Resistor is 1/4 watt carbon film 20ohm +/- 5% variety
Shift register on resistance is rated at 6.5ohm at 50ma at temp of 25c
I agree with him that he should use a 33ohm resistor for safety sake,
but would like debate resolution over using a mA meter
So, what's the collective opinion on this?
--
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)
"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"
" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "