Model 78 and 78-1
Technical Manual
Section 4
Ludlum Measurements, Inc.
Page 4-1
March 2021
Identification of Controls and
Functions
Display
The Model 78 utilizes a four-digit LCD readout with a fixed decimal point. The
two smaller digits located in the lower right corner of the display indicate
exponential power when in the parameter setup mode. The
upper right of the LCD exhibits units and multiplier(s) R/hr,
mR/hr, or µR/hr; Sv/h, mSv/h, or µSv/h; C/m, kC/m, C/s, or
kC/s. However, normally only units of R/hr, mR/hr or µR/hr
are used. The bottom part of the readout displays
ALARM
,
ALERT
,
OFLOW
, and
OVERLOAD
enunciators as well as the low-battery
icon.
Display Status Definitions
ALARM
: ratemeter count has increased above the preset alarm threshold. An audible
continuous tone will accompany the "latching"
ALARM
condition. Depressing
RESET
will
acknowledge the audible ratemeter alarm. Depressing
RESET
a second time will reset the
ratemeter reading and ratemeter alarm.
ALERT
: ratemeter count has increased above the preset alert threshold. To reset an
ALERT
condition, depress
RESET
once if in the non-alarm condition and twice if in an
ALARM
condition. (The first depression in the alarm condition acknowledges the audible alarm.) The
ratemeter will reset to the minimum displayable reading each time the alert is reset.
OFLOW
(Overflow)
: indicates that the incoming count exceeds the capability to display stable
or reliable readings corresponding to the radiation level being measured. The overflow
symbol (
OFLOW
) will appear when the ratemeter exceeds 100 kcps or if the dead time
correction is greater than 75%.
OVERLOAD
: indicates the detector is being exposed to radiation intensities greater than the
detector maximum operating limit. The overload alarm point is set by adjusting the
OVERLOAD
control located on the CAL/SWITCH BOARD.
Section
4
