Choose the Correct Accelerometer

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

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.

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.

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

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.

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 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.

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.

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.

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.

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.