EEVBlog #46 Gossen current shunts enabled by MOSFETS?

[mzacharias]

My Tektronix TX3 does it that way. Does the Gossen?

[NiHaoMike]

If it's not using relays or manual selection switches, it almost certainly is using MOSFETs. The input circuit generally has a pair of inverse parallel diodes after the input fuse, along with several shunts. The shunt value needed changes depending on the range in order to give a signal large enough for the input amplifier. The selection can be done with manual switches (as in multimeters without current autoranging and the uCurrent), relays (as in some Agilent bench multimeters), or MOSFETs (as in portable multimeters with current autoranging). In a portable meter, a relay large enough to handle the maximum current rating would use too much power, while a MOSFET offers almost as low an insertion resistance and uses almost zero power.