Model 78 and 78-1
Technical Manual
Section 8
Ludlum Measurements, Inc.
Page 8-2
March 2021
Note:
The mR/hr – R/hr front panel toggle switch allows this instrument to have
two sets of operating parameters.
F
UNCTION
S
WITCH
P
OSITION
D
ESCRIPTIONS AND
V
ARIABLES
POSITION 0
:
NORMAL OPERATION
places the Model 78 in the normal
(counting) operating mode.
POSITION 1
:
DEAD TIME
(µs) allows changing the detector dead time
correction for the current detector setup. Setting this parameter to “0”
disables dead time correction. The dead time adjusts from 0 to 9999
microseconds (µs). The incoming counts are adjusted for dead time using
the formula to the left, where:
n = corrected counts per second
m = incoming count per second
= system dead time
POSITION 2
:
CALIBRATION CONSTANT
allows changing the calibration
constant for the current detector setup. The calibration constant (CC)
adjusts from 0.001 to 280 X 10
9
. The calibration constant converts
counts/time base to units/time base.
POSITION 3
:
SERIES CONSTANT
adjusts the calibration of the high-range
tube; typically about 300. Adjustable from 0 to 9999.
POSITION 4
:
NOT USED
POSITION 5
:
AUDIO DIVIDE
-
BY
selects the audible clicks-per-event division
rate for the current detector setup. If the
AUD ON
/
OFF
switch is in the
OFF
position, no audible clicks-per-event will be heard.
This parameter ranges from:
0
Divide By 1
1
Divide By 10
2
Divide By 100
3
Divide By 1000
POSITION 6
:
RESPONSE TIME
allows changing the time constant (TC) for
the current detector setup. If the response is set to “0,” the Model 78
automatically calculates (for variable mode) the time constant based on
m
-
1
m
=
n
