96 Input/Output Modules
Trident Planning and Installation Guide
Pulse Input Module
The following pulse input components are available.
The Pulse Input (PI) Module provides six very sensitive, high-frequency inputs.
The inputs can be individually configured for non-amplified and amplified
magnetic speed sensors common on rotating equipment, such as turbines or
compressors. The PI Module senses voltage transitions from the speed sensors.
Every input transition is sampled, and time is measured for an optimized number
of input gear pulses. The resulting count and time are used to generate a frequency
(revolutions per minute), which is transmitted to the Main Processors.
The type of speed sensor typically used with the PI Module consists of an inductive
coil and rotating teeth. The sensor is physically close to the teeth of a gear on the
rotating shaft. As the shaft rotates and the teeth move past the sensor, the resulting
change in the magnetic field causes a sinusoidal signal to be induced in the sensor.
The magnitude of the output voltage depends on:
• How fast the teeth pass the sensor
• The distance between the sensor and the teeth
• The construction of the sensor
A typical gear has 30 to 120 teeth spaced at equal distances around its perimeter.
The output frequency is proportional to the rotational speed of the shaft and the
number of teeth.
!
CAUTION
A Pulse Input Module uses fully differential, input-signal-conditioning circuitry
which is AC-coupled and has high bandwidth. The circuitry is designed for high-
frequency operation with de-bounced edge detection, but is still sensitive to any
type of waveform distortion that could result in erroneous measurements. The
module counts transitions by examining one edge of each pulse. Therefore, ringing
on the input signal can result in many additional transitions being counted. The
module is capable of counting over 32,000 transitions per second.
Model Description Frequency Range Type
3381 Pulse Input Module 0.5 Hz–32 kHz Commoned
2381 Pulse Input Baseplate Direct Termination
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