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Section V

calibrated, set the REL. REF

adjustment to the fully clockwise

ABSOL U T E posi tion before
beginning the calibration. Always

check and set the bias levels first
before calibration.

5-41. Accuracy and Frequ ency Respons e Calibration.

5-10

a. Calibrate the reference supply in Figure 5-2

with a 1 volt thermal converter according to
the steps in Paragraph 5-17.

b. Disconnect the standard and connect the

test oscillator, the 400E/EL, and the digital

voltmeter as shown in Figure 5-2. Connect a

precision 40dB coaxial attenuator between
the BNC "T" connector and the 400E/EL

INPUT.  When  the  thermal  converter  and
reference  supply  outputs  are  nulled,  the
input  to  the  400E/EL will  be  10mV. Set  the

oscillator frequency to 400Hz and the
400 E/ EL to the 0.01 volt range. Using the

amplitude control as coarse adjustment and

R4 as fine adjustment, increase the oscillator

output until the thermal converter output
nulls the reference supply.

c. Adjust A2R38 for a 400E/EL meter reading

of IOmV ±O. l mV or less.

d. Ad just R2 for a digital voltmeter display of

1.000 ±0.005Vdc or less.

e. Lower test oscillator output and set

frequency to IOMHz. Readjust oscillator
amplitude until thermal converter output

nulls reference supply.

f. Adjust A2C28 for digital voltmeter display

of 1 .000 ±0.04 or less.

g. Lower test oscillator output and set the fre

quency  to  10 MHz.  Disconnect the precision
40 dB  attenuator  and  connect  a  precision
50 dB  attenuator  in  its  place.  When  the

thermal converter and the reference supply

are nulled, the input to the 400E/EL will be
3.162

mY.

Set the 400E/EL RANGE to

0.003 volts.

h. Using the amplitude control as a coarse

ad justment and R4 (Figure 5-2) as a fine

adjustment, increase the oscillator output
until the thermal converter exactly nulls the

reference supply output.

Models 400E/400EL

Adjust S2C2 for a digital voltmeter

indication of 1.000 ±O.04Vdc. The 400E/EL
should read 3.16 ±O. l 58mV.

Check at 6 and 4MHz. Amplitude

can be lowered at 4MHz by mOving

A2Cl i and C13 closer together.

j. Lower the test oscillator output and set the

frequency to 400Hz. Replace the 1 volt

thermal converter with a 0.45 volt thermal
converter, and calibrate it according to the

procedure in Paragraph 5-17 using a 0.3162

volt output from the dc standard.

k. Disconnect the dc standard and connect the

test  oscillator  to  the  thermal  converter  as
shown  in  Figure 5-2.  Set the 400E/EL range
switch  to  0.001  volts.  Using  the  amplitude
control  as  a  coarse  adjustment  and  R4  as  a

fine adjustment, increase the oscillator
output until the thermal converter output

exactly nulls the reference supply output. At
null, the input to the 400E/EL will be 1 mV
at 400Hz.

m. Ad just A2R44 for a digital voltmeter display

of 1 .000 +0.005 V dc.

The voltage at TP 4 affects fre

quency  response.  If the  frequency
response  is  low  at  10  and  20 Hz
decrease  voltage  at  TP4  (extreme
limits  8 to 12 volts). After changing

voltage at TP4, check high and low

frequency response.

n. If the accuracy and frequency response can

not be brought into specifications with the

preceeding adjustments, refer to Table 5-11

Factory Selected Components.

5·42. Calibration Procedure Using -hp- 745A1746A

Calibrator.

5-43. Calibrate the 400E/EL for frequencies from
10Hz to 110kHz with the test setup shown in Figure
5-1.

a. Set the 745A to the voltage levels and

frequencies listed in Table 5-5, Alternate
Calibration Procedure (omit steps 2 and 3).

Select the proper 400E/EL range.