Neurotechnology Research Systems
© Plexon Inc
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6.6
Vmon scaling and Z conversion
The Voltage monitor scaling control indicates the relationship between the voltage at the monitor
channel and the voltage at the electrode. The behavior of the control depends on whether the
stimulator is in stimulation mode or impedance test mode as described below.
6.6.1
Vmon scaling (Stimulation mode)
When the stimulator function is set to stimulate the voltage monitor scaling is expressed as the
number of volts at the monitor channel output for each volt at the electrode. By default the scaling
is 0.25 V/V meaning that a 1 V signal at the electrode will appear as 0.25 V on the monitor channel.
This setting is appropriate for most electrodes. Adjusting the Vmon scaling might only be necessary
to help resolve small voltages when stimulating with extremely low impedance electrodes. Divide
the voltage observed on the monitor output by the scale factor to determine the voltage at the
electrode. Note that if the Vmon scaling is set higher than 0.25V/V, then the output of the voltage
monitor will saturate before the compliance limit is reached and the may not reflect the actual
voltage at the electrode. See section 7.7, Voltage Monitor, for additional details.
6.6.2
Vmon scaling (Z test mode)
When the stimulator function is set to impedance test (Z test) a 1 kHz ±100 nA sinusoidal current is
applied to the electrode and the resulting peak to peak voltage elicited across the electrode
indicates the impedance of the electrode. Adjust the Vmon scaling control to obtain the largest
peak to peak signal on the monitor channel that is not clipping. Measure the peak to peak
amplitude of the signal on the voltage monitor in millivolts and multiply the reading by the scale
factor to obtain the electrode impedance in Ohms:
+266 mV @ V
MON
= 1.06V @ electrode
856 mV
pp
@ V
MON
= 34240 Ohm