[R-390] URM-90 LCR bridge question (OT)

Tue, 24 Jun 2003 09:04:59 -0700

Does anyone have a spare manual for the  ZM-11/U?

73 de Bill, AB6MT
[email protected]

----- Original Message -----
From: [email protected]
To: [email protected]
Sent: Tuesday, June 24, 2003 6:19 AM
Subject: [R-390] URM-90 LCR bridge question (OT)

I've used a URM-90 for a number of years and have found it to be highly
accurate, effective, and pretty straightforward to use. The built-in 1000 Hz
generator is adequate for most all purposes.

The URM-90 is not really great for extra-low values of inductance and
capacitance (<10uH, <100pF) but it's adequate. For RF-scale values you're
better off with a grid dip meter (or a Q Meter if you want to get really
fancy).

Where the URM-90 really excels is making up or picking precision value
capacitors from, say, 1000pF to 0.1uF to make up audio filters, phase shift
networks, or timing circuits. It also works well in sorting through junk box
inductances, expecially chokes and iron-core audio frequency stuff.

A more generally desirable instrument might be the ZM-11/U R-C-L bridge. It
has only about half the accuracy of a URM-90, but it allows you to make
leakage measurements at voltages up to 500 and also permits you to measure
the value of an electrolytic capacitor with a DC voltage impressed on it.
It's probably more useful than the URM-90 in determining the "GOOD - BAD"
state of a capacitor. It also seems a little easier to use than the
URM-90 -- takes less time to find the balance point.

Like the URM-90, the ZM-11 uses an internal 1000Hz oscillator as the signal
source. The main difference apart from precision is that the URM-90 permits
the DC measurement of resistors, while the ZM-11 uses AC for all
measurements.

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