# 2-phases connected to single rectifier

I have come across an unusual part of a circuit that I hope someone could shed some light on and I have redrawn in LTSPICE. The circuit is to measure voltage of a 3-phase generator. Two of the phases R and S are measured and applied to the rectifier shown below. The "+" and "-" are then fed into a differential amp. It is unusual to see the second phase applied to the lower half of the circuit shown.

Why would this configuration be used and is there any advantages/disadvantages to using it this way.

• That milliohm resistor is ... concerning. There may be disadvantages to that part. – Brian Drummond Feb 22 '18 at 15:48
• @Brian Those two diodes in series hurts my eyes too. – winny Feb 22 '18 at 19:16
• Welcome to EE.SE! Please show where you find said circuit so everyone can avoid it and state your question. – winny Feb 22 '18 at 19:18
• Just to clarify @BrianDrummond's comment (in case you're not aware of it), 1m is the same as 1 milli. If you want 1 mega, then you have to write 1meg, or simply 1e6. Note that SPICE, in general, is case insensitive. – a concerned citizen Feb 23 '18 at 8:06
• Is this 3 phase Y-connected or delta-connected? If delta, then you may not have a "common" or ground, and connecting across two phases is the only way to read the voltage. Also, the two diodes in series could be there to split the reverse bias voltage across them, or perhaps for reliability (diodes usually fail shorted, so the circuit still works and doesn't short out if one diode fails). – Michael Gorsich Feb 23 '18 at 10:13