spuffock

I need an amp for calibration purposes. It needs to stay an amp for an hour or so, not go wandering off to .999A or 1.001A due to things warming up.
100uA accuracy would be nice.
Any ideas?

ericgibbs

hi,
A good site for this type of info is: www.analog.com

The 'chopper' type opa's are suitable.

http://www.analog.com/library/analog...-02/demystify/

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

spuffock

I'm using a chopper amp in the project already. They seem to work like it says on the box. Incredible. I may well be going to strip the guts out of my old Time Electronics current source and build something better.
I thought, for the amp, I might have to build something, but how do you measure an accurate amp anyway? Maybe buy a new multimeter and trust to its accuracy is the best I can do without a fortune?

ericgibbs

hi,
You could buy a DVM with a calibration certificate.. it costs!

The problem is not only checking your 'standard ref opa' with a calibrated DVM, but the equipment that you are checking!

Can I ask what are you using it for?

EDIT: you could use a voltage reference: http://www.rhopointcomponents.com/pr...+REFS+AND+REGS

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

spuffock

I'm being a bit silly, trying for more accuracy than I need. Another project that I'm working on will have issues concerning battery life, so I thought I might build a milliamp-hour meter. So far it seems to have the capability of fairly good accuracy, and I thought I might push it to see how far it would go.I am at present writing a routine to cancel the offset due to the chopper amp! This might end up as a project for others to build yet, but I picked up a load of LCD displays at a rally, they use a 36 bit word synchronous serial interface, and I might have to redo that bit to use something obtainable.