Model 78 and 78-1
Technical Manual
Section 2
Ludlum Measurements, Inc.
Page 2-3
March 2021
Expose the detector to a check source if the background count is too low to generate a display
reading. Place the
AUD ON
/
OFF
switch in the
ON
position and confirm the external unimorph
produces an audible click for each event detected (audio divide by "1" parameter). The
AUD
ON
/
OFF
switch will silence the clicks if in the
OFF
position.
Note:
It is recommended to use the SLOW response setting when measuring low
radiation fields.
Increase the source activity or lower the alert and alarm points to initiate an
ALERT
and
ALARM
condition. (Refer to Section 8 for parameter change procedures.) Depress the
RESET
to
acknowledge the audible alarm
Decrease the radiation activity below the
ALERT
and
ALARM
threshold and depress
RESET
to
clear the alarm conditions. If an alarm condition is not present, depressing
RESET
the first time
will reset the alert condition and zero the ratemeter.
Position a check source to produce a reading of 0.5 to 2.0 mR/hr (0.005 to 0.02 mSv/h) while
observing the ratemeter fluctuations, select between the fast and slow response time
(
FAST
/
SLOW
) positions to observe different variations in the display. The
SLOW
position should
respond approximately five times slower (for fixed response mode) and three times slower (for
the variable response mode) than the
FAST
position.
Note:
The slow response position is normally used when the Model 78 is displaying low
numbers that require a more stable display. The fast response is used at high count
levels.
Depress and release the
BKLITE
switch. The backlight located behind the LCD should
illuminate for pre-programmed "
ON
" time.
Select the desired
FAST
/
SLOW
and
AUD ON
/
OFF
parameters and proceed to use the instrument.
Note:
The warm-up time on this instrument is less than 10 seconds on every range.
