Ludlum Measurements 3100, Руководство пользователя

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4-4
4.2.11 Power Supply.
The equipment is capable of operating from 115 VAC 50/60 Hz power or from internal
AA-sized batteries . Input AC power passes through a circuit breaker and is applied to a power supply board that
regulates it to a co12 VDC supply. While the instrument is operating with AC power applied, the internal
batteries, if low, may be recharged with a constant (approximately 200 mA) circuit. The +12 VDC regulated voltage
provides input power to the main board, which produces 5 VDC and several other voltages. The power supply also
has a relay to activate the tritium chamber heater when in the PURGE mode, as well as signal relays that provide
contacts for remote indication of alarm and sampling conditions.
4.2.12 Primary AA Batteries.
The instrument may be operated from internal AA batteries, mounted in a battery
compartment at the bottom of the instrument. See Section 6.2 for replacement of these batteries. Nickel-metal
hydride (NIMH) or alkaline batteries may be used. Note that the battery compartment does also contain a self-
resetting fuse (a positive temperature coefficient resistor) designed to protect the batteries from short circuits. The
batteries can be either rechargeable or non-rechargeable. Ensure the selector switch is switched to the correct type.
4.2.13 Amplifier. The output of the electrometer is applied to the range-dependent amplifier on the main board
for current amplification to input to the A/D converter of the microprocessor. This amplifier provides three levels of
gain, adjusted by the microprocessor for the three ranges of measurement from 0-100 µCi/m
3
, 100-1000 µCi/m
3
, or
1000 to 10,000 µCi/m
3
(or Bq/m
3
equivalent). The microprocessor uses the serial communications lines SDI and
SCL to communicate with the transflective LCD (liquid crystal display).
4.2.14 Processor. The processor is located on the main board and is responsible for handling all the inputs and
outputs of the instrument. The instrument’s firmware is stored in flash memory on the processor. The processor also
has variables and parameters that may be adjusted via software. Inputs to the processor include analog voltages
representing temperature, pressure, chamber bias, and the amplified electrometer signal. The outputs include a
pulse-width-modulated (PWM) output for an electrometer offset, as well as digital outputs to turn on the internal
heater and the airflow pump.
4.2.15 Pressure Sensor. The pressure sensor is located on the main board and produces an analog voltage
related to the atmospheric pressure. This voltage is measured and utilized by the microprocessor to make
compensations for the variation in air density.
4.2.16 Display. The display, located on the front panel, supplies status and measurement information to the user.
The tritium concentration level, which can be displayed in µCi/m
3
or Bq/m
3
, is displayed in a large font. Other
information, like current temperature or pressure, is less prominent. The display has a backlight, controlled by a 295-
degree rotary control on the front panel. The display is controlled by a serial interface by the microprocessor.
4.3 PUMP AND AIR FLOW SYSTEM.
The air flow system is shown in Figure 4-4. Air is drawn into the instrument through the input particulate filter. The
air then moves to the mass airflow sensor and then to the airflow DESICCANT SWITCH. When the switch is in the
IN-LINE position, the air flows through the desiccant chamber, which dries the air. When the switch is in the OFF-
LINE position, the air bypasses the desiccant chamber and goes straight to the tritium ion chamber. The tritium ion
chamber detector is where the ionization, occurring while the air containing tritium is in the detector, is collected as
ionization current. This current is proportional to the tritium level in the chamber. If the gamma background
radiation is compensated for, this tritium chamber current is exactly proportional to the tritium (or other radioactive
gas contamination present in the air stream). The air is then removed through the pump and then to the OUT outlet.
The pump operates on a regulated direct current voltage provided by the power supply on the main board.