Page 4 - 1961 , Volume v.12 n.9 , Issue May-1961

sents the time interval between like-
polarity zero crossings of the input
wave-form times the number of pe
riods averaged.
Multiple-period-average measure
ments also give an improvement in
measuring accuracy in cases where a
low-frequency sine wave signal is
accompanied by noise. This occurs
because the trigger error caused by
noise is also divided by the number
DECADE DIVIDERS of periods measured.
Fig. 6. Block diagram of counter circuit arrangement RATIO MEASUREMENTS
for ratio and period measurements. Ratio measurements are also made
with the counter in the period or
needed to provide the following results in ample power gain for multiple-period average function
three functions: driving the associated Nixie® indi modes. To make direct ratio meas
(1) Storage: To achieve count in cator tube. urements it is necessary only to apply
formation storage, the photoconduc- Fig. 5 is a picture of an -fip- deci the frequency representing the ratio
tive matrix is excited by 4 pairs of mal counter assembly showing the numerator to the external counted
neon lamps. Each pair is connected molded lamp block assembly, the frequency connector at the rear of
through transfer diodes to a count readout display tube, and the asso the instrument and the frequency
ing flip-flop in such a manner that ciated counting circuitry. representing the ratio denominator
one and only one lamp is on when to the signal input jack. In this way,
the transfer gate is closed. The lamp MULTIPLE-PERIOD AVERAGE the counter reads Ã-i/h X the period
pairs thus act as storage elements for With the function switch in one multiplier factor as determined by
the position of the function selector
the information gathered by the of the multiple-period average posi
counting flip-flops. tions, the gate circuitry is controlled switch. Again, the accuracy is im
(2) Decoding: Each lamp-pair by the input signal and the count proved directly as the number of
with its associated photoconductive frequency is the frequency of the periods of fo averaged. The block
segments acts as a multi-contact re time base oscillator (100 kc for the diagram of Fig. 6 shows the input
arrangement for ratio measurements.
lay equivalent to one branch of a 300 kc counters and 1 me for the 1.2
relay-tree matrix. Thus the photo- me counters). The number of peri
conductive matrix provides 10 dis ods to be averaged is determined
tinct output connections from the by the number of decade dividers
four bits of binary nformation through which he nput ignal
i
t
i
s
stored in the lamp pairs. passes before being sent to the gate
(3) Amplification: The total re control circuitry. The count dis
sistance change in the matrix output played on the readout then repre-
Fig. 8. New arrangement of column-
type readout is shorter vertically and
easier to read.
DECADE DIVIDERS
The gate timing circuitry has been
designed using digital decade divid
ers capable of operating over a wide
frequency range.
Besides eliminating any need for
time-base divider adjustment, these
. 6 . 8 1 . 0 1 . 2 1 . 4 1 . 6 2 . 0 2 . 2 2 . 4 dividers improve the accuracy of
FREQUENCY (MC)
multiple-period average and ratio
Fig. counter with sensitivity measured on new 1.2-megacycle counter compared with
rated values. With some increase in drive counter measured to well above ratings. measurements by several orders of
Similar improved performance over ratings is exhibited by 300-kc counter. magnitude.
4
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