More on test equioment.
ard at p850ug1.demon.co.uk
Fri Jan 6 19:35:54 CST 2006
A couple of things I forgot to put in my other message.
Firslty, another instrument that you _need_ is a bench PSU. Adjustable
voltage (at least up to 12V, preferably twice that), and at least 5A,
with current limiting. You will find this invaluable for powering up
logic boards outside the main machine, temporarily substuting for battery
packs, testing motors, solenoids, etc. running motors when doing
mechancial alignments, and so on.
One somewhat unconventional use I put mine to recently was to 'lock' a
stepper motor. By connecting one winding of the motor to the PSU and
turning up the voltage until a moderate current flowed, I could lock the
motor spindle and thus the pulley on said spindle. Running the steel
cable that went onto that pulley and which operated the pen carriage in a
ploter was a lot easier with the motor locked.
Secondly, 'good' does not mean 'lots of features'. Many such features are
little more than gimmicks to be mentioned in the advertising. For
example, many digital multimeters have a transistor Hfe range. Since I
have no idea what collector current is used, this is somewhat useless. If
I need to test a transistor, I will use my real transistor tester (a Tek
575, OK...). You can do a quick go/no-go test on a transistor using the
diode test range to make sure the junctions are still intact and not
shorted, of course.
[OK, there is one use for the Hfe range. Once you've used the diode test
range to (a) determine the polarity) anf (b) find the base lead, connect
it to the meter (Hfe range) with the base going to the right socket and
the other 2 leads going to the emitter and collector sockets. Try it with
the latter both ways round. The connection that appears to give the
higher Hfe is likely to be the correct one. No, it's not a substitue for
looking the thing up in a data book, but if you have a house-coded part
it can be useful...]
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