Ludlum Measurements 3100, Manual, Page: 16 / 57

2-1
CHAPTER 2
OPERATION
2.1 INTRODUCTION.
The Model 3100 is designed for use in applications where the presence or level of
radioactive gas (tritium) must be determined. Radioactive gases, such as tritium, are low-energy beta emitters and
must be brought inside the detector in order to obtain an accurate measurement of the level of radioactivity. The
Model 3100 employs a flow-through type ionization (or ion) chamber and a small internal pump. Air from the
surrounding atmosphere is drawn through the ion chamber, and the level of radioactivity is determined by a
measurement of the ionization current occurring within the ion chamber. Another chamber, measuring the local
gamma ionizations, is connected in parallel but with reverse voltage, in order to subtract out gamma background.
The level of radioactivity in µCi/m
3
( or MBq/m
3
) of the air is displayed on a digital display. The digital display
enables readings to be observed with scale levels of 10
2
, 10
3
, and 10
4
µCi/m
3
of tritium in the air.
Whenever the indicated activity exceeds either of the two user defined levels (Alert/Alarm), a latching, “beeping”
audible alarm accompanied by the text “Alrm” on the display is energized. The alarm audio can be silenced by
pressing the ACK/RESET button once. If the radiation activity decreases below the preset level, a second press of
the ACK/RESET button will clear the “Alrm” text from the display. The Model 3100 may be powered either by
eight AA-sized rechargeable nickel-metal-hydride NIMH batteries, or eight AA-sized alkaline batteries, or be
powered by a mains power cord, connected at the back end of the instrument.
The Model 3100 consists of the following sections: a tritium ion chamber, a gamma compensation chamber, an
electrometer amplifier, range-dependent amplifier, microprocessor with A/D inputs, alarm, display, pump drive and
pump, power supply, and battery charging circuits. The circuitry incorporates diagnostics enabling determination of
the ability of the equipment to perform its intended function. Any failures are indicated by a latching steady audible
alarm accompanied by a unique failure text on the display. In addition, a 20-foot sniffing hose is provided for
monitoring remote locations that are difficult to access. The operator has access to the controls and indicators and is
required to be familiar with their use and presentations during operation of the Model 3100 (See Figure 2-1).
2.2 CONTROLS AND INDICATORS. There are various controls and indicators users should make themselves
familiar with prior to use.
2.2.1 Description of Controls.
The controls are shown in Figure 2-1 and are described following the figure.