Multichannel Systems STG1000 Manual - Manual (Page 63)

Analog Output Signals
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11.4 Measuring Output Signals with an Oscilloscope
For test purposes, you can measure the output signals with an oscilloscope.
Most standard oscilloscopes have a probe with a ground cable. This probe is usually connected to
the oscilloscope via a BNC socket. What you do for measuring the voltage output is the
following: You plug in the standard STG cables into the +U output and the corresponding GND
output. You then touch the open end of the cable from the +U output with the probe from the
oscilloscope, and the open end of the cable from the GND output with the ground cable from the
probe. This means you measure the potential difference between the +U output and ground.
Please note that you need a resistor in parallel to measure the current output properly because
oscilloscopes measure voltages. If the input resistance of the oscilloscope is too low, the voltage
output of the STG will be small as well, and you will not see any signals on the oscilloscope. MCS
recommends a resistor of 10 k
Ω because the output signal of the current output should then be
identical to the output signal of the voltage output. You can use the same test protocol
(regardless of the output mode) for the current and voltage outputs, and compare the signals. As
an alternative, you can also use a resistor that mimics the electrode resistance for testing your
experiments.
What you do is, you plug in cables into the +I output and into the GND output of the STG. You
then use alligator crimps for connecting a 10 kiloohms resistor between the two open ends of
the cables. You then touch the cable on one side of the resistor with the probe and on the other
side with the ground of the probe. That is, you measure the potential difference over the
resistor. You can then calculate the current output according to Ohm's law (U = R * I). For
example, if you stimulate with 100 μA, the voltage over the 10 kiloohms resistor has to be U =
10000
Ω * 0.1 mA = 1000 mV = 1 V.
The following illustration shows four possible combinations of connecting the current outputs on
the front panel of the stimulus generator to the oscilloscope. Again, it is important that unused
current outputs are connected to ground.