There are several variations of the Ludlum Model 177, each with their own features.  See below.  They are frequently used as bench top meters or at control points for frisking. These typically have internal batteries so you can take them anywhere.

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Ludlum Model 177 Alarming ratemeter.  Available in the 177, 177-45 and 177-61 models

The Model 177 is a rugged benchtop ratemeter with alarming capability. These units are very popular for frisking operations at stations where line power is available but can also be used in portable applications for up to 50 hours using the internal rechargeable battery. The 177 supports GM and scintillation type detectors and displays the results on a linear readout analog meter. The audio alarm is adjustable from 0 through 150% of full scale, and is factory set to latching. Reconfiguration to non-latching can be accommodated via a minor internal change. 

Front-panel controls include a four-position rotary switch for selecting each detector decade, an alarm set control, an audio volume adjust, fast/slow response switch, power on/off switch and pushbuttons for count reset, battery test, high-voltage test, and alarm test. The back panel contains the power cord connection and a 9-pin type “D” plug, 6 to 9.6 volts power output, alarm output, pulse output, and a recorder output.

Model 177 Series

Model 177: supports GM and scintillation detectors, linear analog meter, 4-decade range, 0 to 500,000 cpm (other dials available), adjustable audible & visual alarm (Part Number 48-1632)

Model 177-50: supports GM, scintillation, and proportional detectors, logarithmic meter, 5-decade range, 10 to 1,000,000 cpm (other dials available), adjustable audible & visual alarm (Part Number 48-1202)

Model 177-61: supports GM, scintillation, and proportional detectors, linear analog, 4-decade range, 0 to 500,000 cpm (other dials available), adjustable audible & visual alarm (Part Number 48-1382)

Model 177-84: supports scintillation and proportional detectors, dual analog 3-decade meters (alpha range 0 to 1000 cpm, beta range 0 to 100,000 cpm), independent adjustable audible & visual alarms (Part Number 48-2727)

APPLICATION: multi-purpose radiation monitoring, surveying; radiation frisking
COMPATIBLE RADIATION DETECTORS: GM, scintillation

HIGH VOLTAGE: adjustable from 400-1500 volts

INPUT SENSITIVITY: adjustable from -10 to -100 mV

LINEARITY: within 5% of full scale

METER: 2.5 x 2.5 in. (6.4 x 6.4 cm), 1 mA, DC movement
METER DIAL: 0-500 cpm, 0-1.5 kV, BAT TEST
MULTIPLIERS: x1, x10, x100, x1k
CONNECTOR: Series “C” (others available)
AUDIO: built-in unimorph speaker with volume control to provide click-per-event audio or built-in audible alarm indicator
ALARM: indicated by a red lamp and full volume audible tone, greater than 60 dB at 2 ft (0.6 m)
ALARM SET: front-panel locking control allowing alarm to be set at any point on the meter

CALIBRATION CONTROLS: accessible from back of instrument (protective cover provided)

RESET: push-button to zero meter and/or reset alarm

RESPONSE: toggle switch for FAST (2.2 s) or SLOW (22 s) for 90% of full scale reading
DATA OUT: 9-pin series “D” connector allowing for external connections of the following items: battery; unregulated supply; instrument common ground; alarm signal (current sink); pulse out; external background subtract; and recorder output
RECORDER OUTPUT: correlated to meter reading (adjustable to 0 to 1.25 volt at 1 mA)
POWER: 95-250 Vac and 6-volt sealed lead-acid rechargeable battery (built in)
BATTERY LIFE: typically 50 hours in non-alarm condition (battery condition can be checked on meter)
BATTERY CHARGER: battery is continuously trickle charged when instrument is connected to line power and turned on (optional external fast charger is available)
SIZE: 5 x 8 x 6 in. (12.7 x 20.3 x 15.2 cm) (H x W x L)
WEIGHT: 4.2 lb (1.9 kg)

CE CERTIFIED: yes