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USING THE COMBISCOPE INSTRUMENTS 3 - 41
Because the programmed PTPeak and OFFSet values directly affect the trace
values, they can be used to calculate the voltage amplitude of the corresponding
trace samples. As explained in section 3.4.3.3 "Conversion to voltage values", the
voltage amplitude of a trace sample can be calculated from the equations:
Vs = (Ts / 200)
*
PTPeak - OFFSet (for 8-bit sample traces)
Vs = (Ts / 51200)
*
PTPeak - OFFSet (for 16-bit sample traces)
where Ts = the value of the trace sample
and Vs = the corresponding voltage amplitude
The SENSe:VOLTage<n>:RANGe:OFFSet command allows you to specify the
vertical offset for each input channel. After a
*
RST command, the vertical offset
for each input channel is zero.
PROGRAM EXAMPLE:
CALL Send(0,8 "SENSe:VOLTage2:RANGe:PTPeak .8", 1)
’
This sets the peak-to-peak range at 800 mV.
’
So, the vertical sensitivity = 800 / 8 = 100 mV.
’
CALL Send(0,8 "SENSe:VOLTage2:RANGe:OFFSet .1", 1)
’
This sets a positive vertical offset of 100 mV, i.e., 1 division.
3.7.6 Autoranging attenuators
The AUTO RANGE function automatically selects the vertical input sensitivity to
keep the signal amplitude between 2 and 6.4 divisions on the screen. Autoranging
attenuators work independently on the following acquisition channels:
> Input channel 1, 2, 3, and 4 for the PM33x4B CombiScope instruments.
> Input channel 1, and 2 for the PM33x2B CombiScope instruments.
Auto attenuation uses a peak-to-peak calculation to determine the maximum and
minimum value of an acquisition, regardless of the input coupling. When auto
attenuation is switched on for an input channel <n>, the input signal is
automatically forced to AC coupling. Still, it is possible to switch to DC coupling
by programming the INPut<n>:COUPling DC command. However, in that case,
the proper operation cannot be guaranteed.
LIMITATION:
Auto attenuation is limited to 50 mV minimum per division. This minimum
value is used as the noise level to prevent auto attenuation from trying to
adjust noise on an open input channel.
PROGRAM EXAMPLE:
CALL Send(0, 8, "INITiate:CONTinuous ON", 1) ’
Auto triggering
CALL Send(0, 8, "SENSe:FUNCtion 'XTIMe:VOLTage2'", 1) ’
Sets CH2 on
CALL Send(0, 8, "SENSe:VOLTage2:RANGe:AUTO ON", 1)
’
Sets auto attenuation for channel 2 ON and switches to AC signal coupling