Re: ANTIQUE SIMPSON / MINNEAPOLIS-HONEYWELL MILLIVOLTMETER, MODEL W129A2X1

After looking through the available data sheets for Model 127 on

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I think I may have found something...

While the specs may have changed slightly or even significantly over the years, I did notice something of interest...

The unit currently described in the

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describes the following:

DC Millivoltmeters, Self Shielding Movement Option 1: Range: 0 - 50 Approx. Impedance (Ohnms) @ 60 Hz: 10 Model/Size and Catalog Number - 2-1/2" Model 127: 06990

Option 2: Range: 0 - 100 Approx. Impedance (Ohnms) @ 60 Hz: 20 Model/Size and Catalog Number - 2-1/2" Model 127: Available on special order.

With regards to the unit I recently procured, it would seem to have some unique design features that may not necessarily be available on current models offered by Simpson Electric, Co.

The meter in my possession is of the 2-1/2" variety and is accompanied by four (hardwired) test leads attached to four connecting posts on the back of the meter.

According to the accompanying detail within the lid of the unit's case...

There is a plain (common) wire. This would have been connected to the inner thermocouple lead or white powerpile lead.

There is a black (0-50 MV) lead. This would have been the outer thermocouple lead.

There is a red (0-500 MV lead. This, in conjunction with the yellow (meter) lead would be connected to the red powerpile lead.

There is a yellow (0-1000MV) lead. This, in conjunction with the red (meter) lead would be connected to the red powerpile lead.

From the detail listed on the underside of the lid, this particular unit seemed to have been used for diagnostics with regards to the thermocouple and/or powerpile of a boiler (based on my google research). Other part numbers in the printed on the detail seem to reference various (deprecated) Honeywell thermocouples and powerpiles.