DIGITAL VOLTMETER - F6FZK - Free

Model 3455A
voltage and vmier controls for a zero reading on the
null meter.
r. Downrange the Null Meter and adjust the
Reference Divider's course and fine controls for a null is
obtained on the 3 rnicrovoIt range.
s. Set the Reference Divider's Standard Cell switch to
Open. Allow ten minutes for the Reference Divider to
warm-up and stablize.
t. Set the Reference Divider's Standard Cell switch to
Momentary and, if necessary, readjust the fine control
for a nu11 indication. Release the Standard Cell switch.
u. The 3455A reading should be within the Test
Limits given in Table 4-3. (1000 V, I kV range), verifying
the full-scale accuracy at + 1 0 V with High
Resolution on.
AUTO-CAL may have to be turned off
when making measurements on the 100 Y
and 2000 V mges. This is only necessary
when using o DC Standard sensirive lo a
changing load impdunce.
Table 4-2, DC Accuracy TW (High Wmalation OW.
3455A 24 Hour 90 Day
Test Limits Test Limits
10 V a 9.9997 to 10.0003 9.9994 to 10.0QO6
NOTE
Each lime the Reference Divider Output
Votrage setting is changed, check for null
and, if necessary, readjust the Reference
Divider's fine control to obtain a null indica-
tion.
Always downrange the Reference Divider
befoe downranging the 3455A. When
upranging, always upran;ge the 3455A before
upranging the Reference Divider.
24 Hour
'For positive readings only. Do not apply negative voltages greater
than - 500 V dc.
Section IV
v. Set the Reference Divider's Output Voltage and
3455A RANGE to each setting (100 V and below) listed
in Tables 4-2 and 4-3 with High Resolution on or off as
indicated. Aa each setting, the 345SA reading should be
within the Test Limits given in the table. (Be sure to
maintain null when the Reference Divider" output is
changed.)
In the fdawing tests for negative readings,
the inpur lo the 3455A mrrsf nor exceed -500
V dc, due to the k 500 V guard f o chassis
limitation,
w. Downrange the dc standard to 1 Y output and
turn off the dc standard's output. Reverse the polarity
of the 3455A INPUT connection to obtain negative
readings. Turn the dc standard's output back on. Verify
the negative dc accuracy for all settings 100 V and
lower. Again, do not apply more than -500 Y dc to he
3455A INPUT.
4-32. The 3455A ac voltmeter accuracy can be verified
for frequencies up to 100 kHz on a11 voltage ranges us-
ing an AC Calibrator such as the -hp- Model
745A/746A. To minimize measurement uncertainties
for frequencies below 50 Hz and above 20 kHz, the AC
Calibrator should be calibrated and its error measure-
ment control should be used to adjust out the errors in-
dicated on the calibration chart. For example, if the
calibration chan indicates that the 74% output is
0.04% high at 1 V, 50 kHz, set the 745A error measure-
ment control to + 0.04% to obtain a precise 1 V output.
The 745A/746A can be calibrated during a routine pw-
forrnance test using the procedures outlined in the
745A/746A Operating and Service Manuals. Calibra-
tion charts for these instruments are normally valid for
at least 30 days.
4-33. A Test Oscillator such as the -hp Model 652A can
be used to verify the ac voltmeter accuracy of the 3455A
for frequencies above 100 kHz (specified for 1 V and 10
V ranges only). The required accuracy can be obtained
by adjusting the Test Oscillator output so that the
3455A reading at I0 kHz is the same as the reading ob-
tained with the highly accurate AC Calibrator. This
reference level can then be maintained to within 2
0.25% over the 100 kHz to 1 MHz range using the
expanded-scale meter on the Test Oscillator. If higher
accuracy is desired, an ac-to-dc thermal triinsfer techni-
que (Figure 4-3) can be used.
4-34. Twt Proeedun.
Equipment Required:
AC Calibrator (-hp- Mode! 745A/746A)
Test Oscillator (-hp Model 65ZA)