Purchased a mA analog meter panel mount no shunt required I went to test my driver and final and the meter pegs any help would be appreciated.
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Meter Help
- Thread starter kaos513
- Start date
Needs a shunt resistor.
Just one problem. You need two numbers to calculate the resistance value required.
The meter's full-scale sensitivity current. For now, I'll guess what you meant was one milliamp. It's typical to find "fs=" in small print at the bottom of the meter face followed by a current rating.
The coil resistance of the meter. This dictates the actual voltage that will push 1 milliamp through the meter coil. If it's 1000 ohms, you need 1 Volt.
If it's 100 ohms, you need only 1/10 of a Volt.
Once you have these two numbers, calculating the resistance value needed for your shunt can be done.
We use a cheap digital multimeter that has a 20-Amp scale and use that scale for setting final/driver bias. That way if a gator clip comes loose and touches grounded metal for a moment, no damage is done to the meter.
Your meter will be at risk if this happens unless it has a fuse or some other sort of overload protection.
Sometimes the build-it-yourself solution is more cost effective. Sometimes not so much.
73
Just one problem. You need two numbers to calculate the resistance value required.
The meter's full-scale sensitivity current. For now, I'll guess what you meant was one milliamp. It's typical to find "fs=" in small print at the bottom of the meter face followed by a current rating.
The coil resistance of the meter. This dictates the actual voltage that will push 1 milliamp through the meter coil. If it's 1000 ohms, you need 1 Volt.
If it's 100 ohms, you need only 1/10 of a Volt.
Once you have these two numbers, calculating the resistance value needed for your shunt can be done.
We use a cheap digital multimeter that has a 20-Amp scale and use that scale for setting final/driver bias. That way if a gator clip comes loose and touches grounded metal for a moment, no damage is done to the meter.
Your meter will be at risk if this happens unless it has a fuse or some other sort of overload protection.
Sometimes the build-it-yourself solution is more cost effective. Sometimes not so much.
73
It also depends on where you insert the meter. It must be isolated from RF thru the choke that feeds the transistors. You cannot insert it on the RF hot side as the RF will drive the meter crazy.
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