Model 272D Digital Remote
February 2016
page 1
1. GENERAL
The Model 272D Digital Remote is a remote status instrument for the Ludlum Model 375 series of
Area Monitors. A large four-digit LED (light emitting diode) display shows the current radiation
reading from 0.1 to 9999 in the same display units as the Model 375. The Model 272D also shows
the current status of the Model 375. The LOW ALARM, HIGH ALARM, SYSTEM OK, and DET
FAIL status indicators are all provided. The audio has a toggle switch that allows the audio to be
enabled or disabled. A pushbutton RESET switch allows the alarm on both the Model 375 and the
Model 272D to be reset.
If the Model 272D becomes disconnected from the Model 375, or loses communication with the
Model 375, after 15 seconds, the Model 272D blanks the display, lights the DET FAIL indicator,
and activates the relay and audio. Upon restoration of communication, the Model 272D resumes
normal operation automatically.
A form C relay connection (providing common, normally open, and normally closed contacts)
enables further alarms to be triggered on HIGH ALARM and FAILURE status. The internal relay
is configured to be fail-safe. The fail-safe configuration is where the relay is activated when the
status is normal. The relay is deactivated whenever the power is off or the status changes to the
alarm or fail conditions. Connections to the relay are provided through a three-pin circular
connector. A short pigtail cable with the mating connector is provided.
A communications cable is supplied to connect the Model 375 and Model 272D. The Model 272D
is powered with a wall-mounted 5 Vdc regulated supply capable of supplying more than the typical
0.5A needed by the Model 272D.
2. CABLES
1. CABLE WIRE-UP FROM MODEL 375 TO MODEL 272D (8303-765)
MALE PINS--MODEL 375 MALE PINS--MODEL 272D
9-PIN D-SHELL CONNECT. W/3 PINS 9-PIN D-SHELL CONNECT. W/3 PINS
4 TXD/RXD 4
8 RESET 8
2 GND 2
2. FORM C RELAY CABLE (8303-722)
Three pin circular connector pinouts and wire colors:
PIN 1-WHT-normally open
PIN 2-BLK-common
PIN 3-GRN-normally closed
The relay contacts are rated for 240VAC, 1 amp max.
