Efficient Plant July 2018 - 33

instrumentation

Choose the Correct
Accelerometer
Answering eight questions on how and where an accelerometer is to be used
simplifies the selection process. Photo: IMI Sensors

1. WHAT TYPE OF DATA IS REQUIRED?
Raw or overall data: An accelerometer's VAC signal is a dynamic
signal on which frequency analysis can be performed while a vibration transmitter's continuous 4-to-20-mA signal of overall values
can connect directly with PLC, DCS, and SCADA systems.
Acceleration, velocity, or displacement: The appropriate measurement range depends on the frequency of the measured vibration.
+ displacement: 0 to 10 Hz
+ velocity: 10 to 2,000 Hz
+ acceleration: greater than 2,000 Hz.
2. WHAT IS THE VIBRATION AMPLITUDE?
The maximum amplitude of the measured vibration will determine
the sensor's measurement range.
+ common accelerometer ranges: 10, 50, 100, and 500 g
+ common vibration-transmitter ranges: 0 to 1 and 0 to 2 ips;
0 to 5 and 0 to 10 g
3. WHAT IS THE VIBRATION FREQUENCY?
Low-frequency response: Most industrial sensors will have a limit
near 0.2 Hz.
High-frequency response: Sensors have a resonant frequency at
which the signal is amplified, leading to sensitivity changes and
possible saturation. To combat saturation, most industrial accelerometers have single- or double-pole RC filters.
4. WHAT IS THE TEMPERATURE OF THE

ENVIRONMENT?

Determine the highest and lowest temperatures to which the sensor
will be subjected.
+ -65 F to 250 F: Most general-purpose industrial sensors with
integral electronics can operate in this range.
+ 250 F to 325 F: High-temperature sensors with special integral

JULY 2018

SELECTING ACCELEROMETERS for specific applications need
not be difficult. Meredith Christman of IMI Sensors, Depew, NY
(pcb.com), says the process basically involves answering eight questions.
- Jane Alexander, Managing Editor

electronics are available since higher temperatures can harm
built-in electronics of general-purpose units.
+ >325 F: Charge-mode designs without built-in electronics are
available.

5. WILL THE UNIT BE SUBMERSED IN LIQUID?
Depths <1,700 ft.: Sensors with integral cables can be permanently
submersed without additional testing.
Depths >1,700 ft.: Sensor should be pressure tested for one hour.
6. WILL THE UNIT BE EXPOSED TO CHEMICALS?
Sensors: Industrial designs feature corrosion-resistant
stainless-steel housings.
Cables/connectors: Check a chemical-compatibility chart. With corrosive chemicals, use PTFE cable with non-corrosive connectors.
7. DO YOU WANT PRECISION OR LOW COST?
Calibration: Precision sensors receive a full calibration. Low-cost
designs receive single-point calibration.
Tolerances: Precision sensors have tighter tolerances on specifications such as sensitivity, i.e., sensitivity tolerance of ±5% versus
±10% for low-cost designs.
8. ARE SPECIAL APPROVALS REQUIRED?
Most industrial sensors can be certified as intrinsically safe for potentially explosive areas. Compare the type of approval needed with
a sensor's published approvals to ensure it meets your particular
requirements. EP

Meredith Christman is a product-marketing manager with IMI
Sensors, a division of PCB Piezotronics, Depew, NY. Learn more about a
range of condition-monitoring solutions at pcb.com.
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Table of Contents for the Digital Edition of Efficient Plant July 2018