thanks for the reply MrAi,
for the moment i have a circuit diagram of voltmeter and an ammeter,which is working fairly well with the proteous simulation(although still i couldn't extend it to several ranges).i have some experience with pic 16f84A chip but since it has only one ADC pin i thought to go for 16f877A chip.and also regarding mathematics,i think it wont be a problem ,coz im in 3rd year of my engineering course and i almost completed all the mathematics courses prefered.
i dont know how to attach my circuit diagrams here,if there is that facility im willing to attache my circuit diagrams here.........
and also if anybody has any circuit diagrams related to this plz post it.......
im bit confused....I designed an I-V converter and the LabVIEW application implemented auto-range. Nothing really magic, but I had a -10 to 10 V linear output V. The actual range was probably higher and relays to select the range. So, you just keep bumping the range until you get something between 1 and 10 volts or -1 and -10 volts or your at the lowest range/highest gain possible.
Protection mechanism were built into the circuit design which is the same you would do for a voltmeter.
Total cost was about $5000. It used 2 system DMM's, one 4 channel system DMM (3 used) and had suppression and biasing capability. It was also 2 or 4 terminal. 4 ranges: 100 mA, 10 mA, 1mA and 0.1 mA FS. 3 dual tracking power supples and one logic supply.
Designed primarily as an analog Front End. It was stable into capacitive loads.
It wasn't easy to do and it could have been better. AC measurements (front end) was excellent. DC was good. The 25 uV of offset at the input wasn't compensated for, so I has an error on the order of 25 pA.
1% resistors were used in the FB loop, and calibration constants could be adjusted in software. The AC calibration could too after it was processed by a $5000 lock-in amp.
The inputs were gaurded too.
It also incorporated an AC overload indicator.
Hello again,
Have you read the Microchip app notes on measuring these kind of things? There are some notes on that site that should help you with these circuits.
Hello again,
Have you read the Microchip app notes on measuring these kind of things? There are some notes on that site that should help you with these circuits.
Measuring small value resistors is a problem in itself. Sometimes you need a decent gain amplifier to amplify the voltage across the resistor so you can get a voltage that is high enough to measure with 'normal' equipment or the usual AD input. The gain amplifier amplifies the small voltage up by at least 10 times which then makes it much easier to measure, then you divide by 10 in the algorithm.
What size caps do you intend to measure?
What range of resistances do you intend to measure?
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