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Guest
You have closed AC breaker contacts carrying 10 A that are slightly worn so that they are dropping 20 mV. Bad contacts drop >100 mV.
You have a cheapie DVM with input impedance of 20 megs that can't resolve AC millivolts very well so you want a device of some sort so that this 20 mV is changed into 2 V.
So as not to disturb what you're measuring you don't want the device to draw more than 1% of 10 A from the closed contacts.
Hint:
You already know what voltage gain is required.
The current gain required is [2/(20e6)]/100 mA = 1/10^6 = 10^(-6) so no current gain is required, and the power gain required is 100 x 10^(-6) = 10^(-4) so no power gain is required either, so this device doesn't need a battery or a power source. So much for that UL listing. Yeah!
You will, however, need to know the difference between a series component and a shunt component.
There are three components in this device, not counting wire, solder, a fuseholder and clip leads. One component is a <100 mA fuse and another component is a variable resistor for calibration which is set to give a voltage gain of 100.0 after the fuse is in place. New fuse probably requires new calibration.
What is the third component and how are all the parts wired?
What is the parts cost for this valuable troubleshooting tool, not counting the cost of a box?
Is it durable? Sensitive to temperature? Sensitive to overload? Can it be dropped 3' onto a concrete floor and still work? Is it sufficiently accurate for its application? Are these parts already in your basement or garage? Is it guaranteed not to bust, rust or collect dust?
The first correct answer wins a cheap beer from my basement fridge [planefare is on you].
This is a limited time offer, so hurry. Operators are standing by.
You have a cheapie DVM with input impedance of 20 megs that can't resolve AC millivolts very well so you want a device of some sort so that this 20 mV is changed into 2 V.
So as not to disturb what you're measuring you don't want the device to draw more than 1% of 10 A from the closed contacts.
Hint:
You already know what voltage gain is required.
The current gain required is [2/(20e6)]/100 mA = 1/10^6 = 10^(-6) so no current gain is required, and the power gain required is 100 x 10^(-6) = 10^(-4) so no power gain is required either, so this device doesn't need a battery or a power source. So much for that UL listing. Yeah!
You will, however, need to know the difference between a series component and a shunt component.
There are three components in this device, not counting wire, solder, a fuseholder and clip leads. One component is a <100 mA fuse and another component is a variable resistor for calibration which is set to give a voltage gain of 100.0 after the fuse is in place. New fuse probably requires new calibration.
What is the third component and how are all the parts wired?
What is the parts cost for this valuable troubleshooting tool, not counting the cost of a box?
Is it durable? Sensitive to temperature? Sensitive to overload? Can it be dropped 3' onto a concrete floor and still work? Is it sufficiently accurate for its application? Are these parts already in your basement or garage? Is it guaranteed not to bust, rust or collect dust?
The first correct answer wins a cheap beer from my basement fridge [planefare is on you].
This is a limited time offer, so hurry. Operators are standing by.
