Model 2241-2

Manufacturer: Ludlum
Order / Quote

This instrument is a general purpose, digital ratemeter with a built-in scaler that provides timed counts over a user specified period. This system will store detector setup information for up to two detectors so personnel can easily change detectors in the field. The LCD presents readings in a four-digit moving decimal format together with one of a wide range of available units of measure and is accompanied by several operational and alert icons. The LCD backlight can be activated and remains lit for a user-adjustable interval. This instrument features adjustable alert & alarm setpoints for both the Ratemeter and Scaler modes. Front-panel controls include a rotary switch for selecting between Off, Ratemeter Mode, and Scaler Mode, switches for audio on/off and fast/variable response time, and push buttons for activating the LCD backlight for either resetting the counts or acknowledging any alarms. A locking toggle switch facilitates swapping detectors while preventing accidental switching.

Key Features

  • Digital ratemeter with built-in scaler
  • Auto ranging
  • Panel mounted locking switch for selecting 2 detector setups
  • Adjustable alarms
  • Wide range HV
  • Overrange & overload protection

INDICATED USE: general purpose survey, gross counting

SUGGESTED DETECTORS: GM, proportional, scintillation

LINEARTY: Readings are within 10% of true value with a detector connected.

ALERT/ALARM: indicated by annunciation on display and audible tone

DISPLAY: 4-digit LCD display with 1.3 cm (0.5 in.) high digits, separate annunciators for display units, alert, alarm, low battery, detector overload, counting overflow, and scaler counting

BACKLIGHT: pushbutton to activate

RATEMETER: can display in R/hr, Sv/h, cpm, or cps when selector switch is in RATE position

DISPLAY RANGE: auto ranging from 0.0 μR/hr–9999 R/hr; 0.000 μSv/h–9999 Sv/h; 0 cpm–999 kcpm; or 0 cps–100 kcps

SCALER: adjustable from 1–9999 seconds (in 1-second intervals)

HIGH VOLTAGE: 400–2400 volts

POWER: 2 "D" cell batteries

DISCRIMINATOR: adjustable from 2–100 mV

BATTERY LIFE: typically 200 hours with alkaline batteries (low battery warning on LCD)

SIZE: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x W x L)

WEIGHT: 1.6 kg (3.5 lb), including batteries

The following parameters are adjusted for each detector by a removable switchboard. Once initial setup and calibration have been completed, the switchboard can be removed without affecting normal operation of the instrument.

BACKLIGHT “ON” TIME: 5, 15, 30, 60, 90, 120, 180, or 240 seconds for backlight to stay “ON” when activated

SET MINIMUM DISPLAY: allows lower limit of auto-ranging display to be fixed, for example, display can be set to not show values less than 1 mR/hr

RS-232 DATA DUMP MODE: enables or disables binary dump mode to RS-232 port, when enabled binary data will be dumped every 2 seconds

RS-232 DETECTOR SETUP MODE: allows for detector parameters to be input by RS-232 port

BAUD RATE: 150, 300, 600, 1200, 2400, 4800, 9600, or 19200 bps

DEAD TIME: adjustable from 0–9999 microseconds

CALIBRATION CONSTANT: adjustable from 0.001–280 X 109 counts/display unit

AUDIO DIVIDE: 1, 10, 100, or 1000 events per click


  • Variable: Dependent on number of counts present. Typical times are FAST 4 to 25 seconds, SLOW 4 to 60 seconds (All times stated from 10% to 90% of final reading)
  • Fixed: The parameter is adjustable from 10 to 25 resulting in a FAST response from approximately 2 to 50 seconds. The SLOW response is approximately 10 to 250 seconds. For MDA-type measurements, the fixed response mode is recommended
RATEMETER ALERT/ALARM: set at any value within the effective range of each detector

SCALER ALARM: adjustable from 1–999999 counts

SCALER COUNT TIME: adjustable from 1–9999 seconds

TEMPERATURE RANGE: -20 to 50 °C (-4 to 122 °F)

RS-232 OUTPUT OPTION: Part No. 4408-192: This option requires a firmware change on the instrument to output ASCII data.


DETECTOR SWITCH: two-way locking toggle switch