Specifications
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182011822 Operator’s Manual
Comparison Voltage Operation (VcoMP)
Leave the 1822 set up as in the previous exercise or set
as follows:
+ INPUT DC
- INPUT OFF
HF-3dB POINT No lights on (full BVV)
LF-3dB POINT No lights on (DC)
GAIN Xl0
ATTENUATOR
+1
INPUT RESISTANCE t M
PRECISION VOLTAGE GENERATOR + 0.0000
COMPARISON or DIFFERENTIAL COMPARISON
EFFECTIVE GAIN Xl0
¯ Function Generator output: 50 kHz 50 mVpk sine
wave. connected to the 1822’s +INPUT.
¯ Oscilloscope: Set at 50mV/div (equivalent to 5 mV/div
with 1822 at X10 GAIN) and time/division adjusted for
2 to 3 cycles.
Under these conditions, the display on the oscilloscope
will extend off the top and bottom of the screen.
Press the -INPUT VCOMP button. This internally
applies the Precision Voltage Generator’s output to the
1822’s -INPUT and the OFF light goes out (the
-INPUT connector is disabled).
The positive and negative peaks of the waveform
displayed on the oscilloscope are (respectively)
divisions above and below the display center line. Push
the button above the digit that is two places right of the
decimal (10 mV) in the Precision Voltage Generator
(PVG) until the positive peak of the waveform appears
the oscilloscope’s display. Continue incrementing and
decrementing Precision Voltage Generator’s digits until
the peak of the waveform is at the centerline of the
oscilloscope’s display. The number in the Precision
Voltage Generator display is the waveform’s positive
peak voltage.
Press the + button in the Precision Voltage Generator.
Observe that the negative peak of the signal is now at or
near the oscilloscope’s display centerline. By
incrementing and decrementing the digits, the negative
peak can be positioned to the oscilloscope’s display
center line. Now the number in the Precision Voltage
Generator’s display is the waveform’s negative peak
voltage.
Change the oscilloscope’s sensitivity from 50 mV/div to
10mV/div. Overall sensitivity, including the 1822, is now
lmV/div. Temporarily change the oscilloscope’s input
coupling from DC to GND (or OFF) and re-center the trace
center screen using the oscilloscope’s position control. Return
its input coupling to DC. Now press the XI0 button on the
1822 to invoke its Autobalance function. (Note that pressing
the gain button that is already selected causes the 1822 to
adjust its DC balance, but does not change its gain.)
Change the Precision Voltage Generator’s reading to again
place the negative peak of the waveform at the oscilloscope’s
center screen. Note that the Precision Voltage Generator’s
display represents the negative peak voltage of the waveform
with greater resolution.
Return the oscilloscope’s sensitivity to 50mV/div and press the
1822’s -INPUT OFF (or AC or DC) button. The Precision
Voltage Generator will retain its setting and the display on the
oscilloscope will be centered about the center line. Press the
-INPUT VCOMP button again and observe that the Precision
Voltage Generator’s output is again connected to the minus
input of the 1822’s -INPUT.
Following are a few observations on using the 1822
comparison voltage mode (VCOMP):
The negative input and its AC, OFF and DC coupling are
disabled. Instead of being a differential amplifier, the
1822 becomes a differential comparator. It compares the
voltage present at the +INPUT with the output of the
Precision Voltage Generator and when they are equal, the
output of the 1822 is zero volts.
The value displayed by the Precision Voltage Generator
indicates a waveform’s voltage, with respect to ground, as
it passes through the oscilloscope display’s centerline. It
is very important that the oscilloscope’s trace be
positioned to center screen if an accurate measurement is
to be made using this method.
By using the 1822 in the comparison voltage mode and
the oscilloscope in a high sensitivity setting, highly
accurate voltage measurements can be made.
The Precision Voltage Generator can be used as a position
control which allows the 1820/1822 to operate in its linear
region.
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