Physics and Engineering of Radiation Detection

13.2. Modular Instruments 721

the coincidence logic pulse must arrive at the MCA before the direct pulse from the
detector reaches the MCA. To ensure this a delay amplifier is generally used to delay
the arrival of the amplified detector pulse to the MCA.

Fast Amplifier

Source

Preamplifier

Detector

Preamplifier

Detector Fast Amplifier Timing SCA

Coincidence Unit

Timing SCA DelayAmplifier

MCA PC

Figure 13.1.5: Block diagram of a coincidence system capable of pulse height

spectroscopy.

13.2ModularInstruments...........................

Modular instruments are very popular in research and industrial environments due
to their off-the-shelf applicability and ease in use. The basic idea is to build a whole
data acquisition system by connecting standalone modules. The obvious advantage
of such systems is that they greatly reduce the cost and time involved in application
specific designs and construction. The downside is that they are not suitable for
large scale systems. Also the user is restricted in using the available I/O and con-
trols as designed by the vendor instead of dictating these according to the system
requirements.
In this section we will look at three most commonly used modular systems: NIM,
CAMAC, and VME.

13.2.ANIMStandard

Nuclear Instrumentation Methods (NIM) is an old standard that came into effect
in 1964. The basic idea behind its establishment was to introduce standalone and
replaceable modules, which could be combined together to form a complete data
acquisition system. The convenience of using modules interchangeably without dis-
turbing other parts of the system has been the main source of its widespread use
by physicists and engineers. Even though new standards and modular systems have
been introduced but due to its simplicity of integration and use, NIM is still used
in many places.