| M3a, Critical current measurement
The M3a is an extended version of the M3m, difference is that it has it's own isolation amplifier [iso-out] build-in, making it possible to use two M3a's in one rack. Example: measuring both switching and retrappimg current.
This module makes repetetive Ic(switching current) measurements at dc to kHz speed in combination with a current source module (e.g. S4m) and a voltage measurement module (e.g. M2b).
When a current sweep is made and the voltage across the sample [V-meas] passes a treshold value [Vref] it is assumed to be a switching action. (switching or retrapping, positive or negative can be selected). At that moment the value of the current source control voltage is sampled and hold and presented as a steady voltage [V(Ic)] at the output. So a [V(Ic)] of +1V means a switching current of +100% of the selected range of the used current source. Example: S4m on 100nA/V, so if V(Ic)=0.3V this means 30nA.
Each time an event is detected the [trig] LED flashes and an optical pulse is send via the [fibre-out] output. This [fibre-out] can be used to trigger the voltage-readout multimeter [V(Ic)] or just to count the switching event frequency.A fibre (1mm plastic core, grey coated) can be connected from [fibre-out] to a fibre-TTL-converter box (see picture below) That can trigger the commercial voltmeter (example: keithley 2000) to get 1 synchronised reading per switch event.
The treshold voltage [Vref] has to be applied remote. This treshold be set by a DAC or Iso-amp (selected in the summing module).
The [mode] switch selects the type of event to trigger on (switch+ retrap+ etc).
Picture showing two M3a modules both reading out the same voltage amplifier M2b.
The iso-out and grey fibres going to voltmeter trigger boxes are connected.
The two M3a modules also read both the same current source S4m, not on this picture.
fibre to voltmeter trigger box: