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Keithley 2015 THD

I just picked up a very cheap Keithley 2015 THD multimeter from South Korea via eBay. It showed up today in very good condition — it could do with calibration, but everything seems to work fine on it. The display is quite dim, as is common with older vacuum electroluminescent displays. The good news, though, is this display module is still carried in stock and can be ordered (new!) from the Tektronix spares department for the princely sum of $66. Score! With the not-cheap shipping, new display and even with cal, this comes out as still a pretty good buy.

On the calibration side, I suspect it would cost about $120 to send it out to Simco or some such, which is probably well worth the money. Alternatively, I might actually send out my big HP, get that cal’d, then use that to calibrate the Keithley using a transfer standard. I need to get at least one of these meters done soon anyway.

Anyway, about the Keithley. It’s a full-featured 6.5 digit digital multimeter with the usual compliment of DC and AC voltage and current measurement, 2- and 4-wire resistance measurement as well as a few extra niceties like support for thermocouples, frequency and period measurement, diode checking, continuity, etc. DC/AC volts has a resolution of 0.1 microvolts, current 0.01 microamps. The continuity beep has user selectable sensitivity and is extremely fast responding.  Of particular interest is a BNC on the back which outputs a reference audio signal that when analyzed by the main inputs can be used to measure total harmonic distortion in an audio circuit. It’s possible to do THD measurement with a spectrum analyzer or a scope with FFT capabilities, but this thing is essentially a 1-button test.  Other than this, it’s built as a system DMM, so it has an extra set of probe connections on the back along with pretty extensive GPIB and front-panel programmability. It’s not quite as cool as the current model Keysight and Keithley meters with graphical displays and built-in data logging, but for the price I’ll certainly not be complaining.