Model 78 and 78-1
Technical Manual
Section 3
Ludlum Measurements, Inc.
Page 3-1
March 2021
Specifications
DISPLAY
: 4-digit LCD with 1.3 cm (0.5 in.) character height
Model 78 RANGE:
0.1 to 999.9 mR/hr
Model 78-1 RANGE:
1 µSv/h to 9999 mSv/h
DISPLAY LINEARITY
: within 10% of true value with connected detector
INPUT SENSITIVITY
: adjustable from 2-100 mV; negative pulse response; normally set to
50 mV through coiled cable
ACCURACY
: digital readout and analog logarithmic meter are accurate within 10% of true
value
HIGH VOLTAGE
: adjustable supply from 200 to 2500 V; regulated to within 0.2% at 1000
Vdc; maximum load of 50 µA at 1000 Vdc; two set-points normally set to 550 Vdc (HV1)
and 550 Vdc (HV2)
RESPONSE TIME
: variable or fixed ratemeter response (All stated times correspond to a
range of 10% to 90% of the final reading). Factory default is ˝variable˝ so that the instrument
will automatically adjust the response time to the best setting for the current count rate
Variable Response
: dependent on the number of counts present; typically 4 to
25 seconds for
FAST
and 4 to 60 seconds for
SLOW
Fixed Response
: The
FAST
response position is programmable from 1-199
seconds. The
SLOW
response position is approximately five times slower than
the
FAST
. For MDA-type measurements, the fixed response mode is
recommended
ANGULAR RESPONSE:
within 30% as detector is rotated from 0 to 90 degrees (calibration
reference is with radiation field parallel to the long axis of the detector)
GEOTROPISM:
referenced to the unit in horizontal position with display up. The indication
will not vary more than 2% of the full-scale reading with the unit in any other orientation.
Section
3
