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

[K2CBY@aol.com]

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.