[volt-nuts] Homebrew DVM

Randy Evans randallgrayevans at yahoo.com
Thu Nov 10 15:45:51 UTC 2011

I am in the process of designing a homebrew DVM that initially will only cover 0 to 12VDC measurement range.  Perhaps in the future it could be expended for a wider range but the issue is getting very accurate and stable (stable is the key operative issue) range divider resistors.  The design is based on the National Semiconductor app note 260, but modified with more modern components such as low charge injection analog switches, faster comparators, LTZ1000 reference, extremely linear integrator,  low cost uprocessor, etc.  My hope is that the DVM will be able to measure to 8.5 digits over this limited range.  We shall see.  It should be a fun project, regardless.
The big issue is the lack of noise rejection characteristics.  A substantial amount of averaging may be required so fast 8.5 digit measurements might be out of the question.  However, it should be a low cost measurement technique for high accuracy measurements of stable voltages.  Obviously, the measurement accuracy would be largely determined by the accuracy of the LTZ1000 reference.
Since the integrator is the key circuit for this design, I would really like to see the integrator design in the HP-3458A, if anyone could provide a copy of the circuit.  Comments on the approach would be apprecitated.
Randy Evans

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