Sect. 11 Page 7
b. Switch the RANGE control to CAL. grating circuit. On low frequency ranges, it is
necessary that the integrating time constant be
c. Adjust the CAL ADJ potentiometerwithascrew- long enough to prevent excessive flutter of the
?
driver so that the meter indicates full scale (10) meter or recorder. This integrating also slows
on the 0-10 scale. down the response of the meter and recorder cur-
rent to sudden changes in frequency onsthe low
60% CHECK ranges.
This check places 6.3V at power line frequency
across the input circuit of the meter. For example, on the 10 cps range, the integrating
time constant is 200 milliseconds. Thus, when
To perform the check, switch the SENSITIVITY the frequency of the input signal changes suddenly,
control to the 60% CHECK position and place the there will be an observable lag in the response of
RANGE switch to a position which includes the the meter or recorder. In fact, after 200 milli-
known frequency of the power line. The line fre- seconds, the meter needle will have moved only
quency should be indicated on the meter. 63 percent of the distance between the old and new
readings. It will move 90 percent of the distance
in about one and a quarter seconds. If the input
2B-10 RECORDER OPERATION frequency varies about its average value in a
sinusoidal manner, the output current will also vary
The Model 500B will drive any 1 ma, 1400 ohm sinusoidally about its average value. The ampli-
(400 ohm) recorder. When a recorder is used tude of this current variation will also be reduced
with the instrument the REC ADJ compensating by the integrating circuit. An integrating time
resistor in the instrument must be adjusted to constant of 200 milliseconds corresponds to a high
match the resistance of the recorder to that of frequency cut-off of 0.8 cycles-per-second. Thus
the meter circuit. The adjustment procedure is as if the input frequency is varying at a 0.8 cps rate,
follows: the resulting current variation will be attenuated
by 3 db, and its phase will lag that of the frequency
a. Allow the 500B to reach a stable operating tem- variation by 45".
perature, and place the SENSITIVITY control inthe
60% CHECK position. Adjust the RANGE switch to The table below shows the integrating time con-
3 include the line frequency, and note reading on stants (T) and cutoff frequency (F0) for various
meter. range settings and expansion conditions on the
500B. The effective rise time (0-90%) of the out-
b. Plug recorder into the RECORDER jack and put current is equal to 2.3T.
adjust the REC control on the front panel so that
the meter indication on the Model 500B is identical RANGE NO EXPAN. X3 EXPAN. X10 EXPAN.
to the reading obtained in step a., above.
10% T=200 ms 18 ms 57 ms
c. Use mechanical adjustment on recorder to ob- qo =0.8% 8.9 3.2 'L
tain reading, above, on recorder scale.
30 % T=5 ms T=18 ms 57 ms
When the recorder is removed from the circuit and F,,=32% F0=8.9% 3.2%
the REC adjusting potentiometer is removed from above
the meter circuit so that the accuracy of the 500B
is unimpaired. The external recorder is placed
in series with the meter in the 500B, and it tracks 2B-12 PULSE OUTPUT RESPONSE
with the meter in the 500B. Thus, expanding a
scale on the 500B simultaneously expands the re- The voltage from the PULSE output terminal can
corder scale. be used to drive a recorder at higher speeds
than are obtainable using the meter current from
the recorder jack. It can be used to drive a stro-
ZB-11 RECORDER JACK RESPONSE boscope or sync an oscilloscope. The PULSE ter-
minal produces voltage pulses which are identical
The current at the 500B recorder jack is pro- in shape to the current pulses used in the meter
portional to the frequency of the input signal. circuit. Since this output signal is direct coupled,
This current is derived from a successionofpulses it contains a dc component which is proportional
and is averaged by means of a simple R-C inte- to frequency. However, the fact that it consists of |
ACEC
