Buying a Simpson 260 Multimeter

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The Simpson 260 is a general purpose industrial grade analogue multimeter made in the USA. It can be found iin the UK under the brand Bach Simpson. There is a lot of information on the internet including repair and operating manuals

A large number of models (or series) but the format is similar. Later models have an option of a more modern plastic case as opposed to Bakelite. Some are designated P which means that there is relay protection and some M which means mirror scale

The Simpson 260 can still be bought as a new item

The moving coil meter movement sits in its own compartment isolated from debris and other contamination from the circuit. It is easy to take apart. The battery compartment is separately accessible. Four long screws hold the case together. There is a single circuit board that can be accessed for repair or cleaning the switches. Even the glass covering the meter is easy to remove and replace. Its easier to disassemble than for example an Avometer. Later models have a taut band meter suspension which I believe is more robust than a hair spring.

There is more scope for calibration. There are easy to use internals pre-sets on the board. One is for basic current setting, one is for DC volts and two are for 2.5V and 250V AC. A decent function generator plus a reference high grade meter (like a Fluke 87) are all that's needs to re-calibrate starting with the basic 50 micro amp DC sensitivity. There are guides available on the internet and one or two videos too. 

Relay Protection.
This is a feature I really like and more than anything differentiates it from the Avometer (which has a purely mechanical cut-out). As long as the 9V battery is installed the meter is protected from overload by a fast action relay. Even if the  voltage slowly increased toward overload (4 x reading max I think) the meter will disconnect and stay that way until it is disconnected or fault remedied. It works on all modes. It is indicated by the P designation and a small white button on the facia (hard to see in most e bay photos).      

You should get between 1 and 1.5% of full scale on any range. The least accurate is the lower part of the 2,5V AC scale. I think this is because (unlike an Avometer) there is no AC transformer so the scale is calibrated to take account of diode non-linearity. The voltage and current ranges are not as comprehensive as an Avometer and it does not measure AC current

What to Buy
Mine is a Simpson model 6 p which has standard banana connectors which I have calibrated to high accuracy easily beyond manufacturers conservative claims. I like the relay protection which is  highly effective. 

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