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At this point, the DA1855A is in the following state:
Setting:
+Input
-Input
BW Limit
Gain
Attenuator
Input Resistance
Precision Voltage Generator
Comparison or Differential
Effective Gain
Press the ÷1 Attenuator button on the DA1855A. The ÷1 Attenuator light is now on.
Check: The DA1855A Effective Gain indicators change when the probe is switched from 10X to 100X.
Note: The DXC100A provides probe attenuation factor information to the DA1855A through an 11" black
wire which should be plugged into the DA1855A Probe Coding Input jack on the DA1855A rear panel. If the
DA1855A has no probe coding input, and the wire is not used. Skip to Step 2.
Note: It is both important and convenient to use the right hardware to connect the probes to the test
signals. In all cases, the BNC to probe tip adapters are helpful. For the high frequency adjustments, they are
required.
CMRR (common mode rejection ratio) adjustments should be done with both probes connected to a BNC T
(two female BNC and one male BNC connected together without any matching resistors).
Note: With the DXC100A connected, let 20 minutes pass to allow the DA1855A to warm up before
performing the calibration procedure.
2. +Input X10 DC Attenuation
Setup: Set the probe to the 10X position. Connect both probes to the BNC T, the BNC T and the DVM to the
dc voltage source. Set the voltage source to 150 volts. Press the V
DVM and note the actual voltage (e.g. 149.821 volts). Set the Precision Voltage Generator to equal the
noted voltage (e.g. 149.821 volts).
Limit to 20MHz. Press the X10 Gain Button (to invoke AUTOBALANCE).
Adjust: R5 (+X10 DC) to bring the DA1855A output to center screen (0 volts) on the oscilloscope. A 1 division
error is equivalent to 10mV out of 150 volts, or 0.0067%, or 67 ppm.
3. X10 DC CMRR
Setup: Continuing from the previous step, press the –Input DC button.
Adjust: R6 (-X10 DC) to bring the DA1855A output to center screen (0 volts) on the oscilloscope. This is a
very critical adjustment, and it is desirable to disconnect both probes from the source simultaneously (by
removing the BNC T) and observe that the trace stays within 0.25 div (60,000:1 CMRR) between the two
conditions.
4. +Input X100 DC Attenuation
Setup: Continuing from the previous step, set the probe to the 100X position. Set the voltage source to 300
volts. Press the V
Comp
the Precision Voltage Generator to equal the noted voltage (see footnote). Set the oscilloscope to 10mV/div
and 10µs/div. Press the +Input DC button. Press the X10 Gain button (to invoke AUTOBALANCE).
1
When a large voltage is not available, or when extra precision is desired, monitor the PVG output on the DA1855A rear panel and set the PVG to exactly
one tenth the voltage applied to the probe. As little as 32 volts may be used to calibrate the +probe using this method. For CMRR, 32 volts is inadequate
and a 50 or 60Hz signal of 30 to 90 Vrms is recommended.
917422-00-RevA
Status:
Off
Off
Full
X1
÷1
1M
+000.00
Comparison
÷100
1
Set the oscilloscope to 10mV/div. Press the +Input DC button. Set the BW
button. Measure DC source with DVM and note the actual voltage (e.g. 302,617). Set
Operator's Manual
button. Measure the dc source with
Comp
7
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