|Re: Any Interesting HP 3421A applications out there?|
Message #8 Posted by Tony Duell (UK) on 22 Aug 2003, 6:44 p.m.,
in response to message #1 by Tracy Vermeyen
I have an HP3421 (great instrument!), but I normally use it with the HP71. That machine has more memory than the 41, which is useful for storing and processing whatever data I measure with the 3421.
One application I use it for is testing the HP chargers. It is well-known that the chargers for the Woodstock, Spice, and Topcat series are just transformers, but they're transformers with deliberately high internal resistance. So i decided to do the stand school experiment with said chargers -- connect various resistors to the output and measure the voltage, then plot the V-I curve.
Of course I've got better things to do than measure voltages all day long. So I connected 8 relays to the digital outputs of the 3421 (I actually used a ULN2803 chip to drive them, this is probably not necessary, the 3421 could do it directly), and used said relays to switch in the resistors in a 7 stage chain (1, 2.2, 3.9, 8.2, 15, 33, 68 ohms IIRC, with a 10 ohm in series with the lot). The last relay disconnected all the resistors from the charger so i could measure the open-circuit voltage.
I wrote a little HP71 program to cycle through the 129 possible resistances (128 settings of the chain, and open-circuit), and record the AC voltage at the output of the charger. These readings were stored in a text file that was then uploaded to my 95LX palmtop (one of the few machines I have with a spreadsheet) to plot the graph.
On other thing I did was to use the resistance ranges of the 3421 to measure the resistance of the chain in each of the settings, and saved that on the 71. That way I could get away with cheap 10% power resistors.