Instrumentation and Controls Technicians: When your critical pumps, motors, or compressors are protected with 4-20
mA vibration sensors, how can you be sure that those sensors are working properly? Vibration testing need not be more complicated than other types of testing that you perform every day. Do you use a hand pump to apply a known pressure to your 4-20
mA pressure sensors in the field? With The Modal Shop’s Portable Vibration Calibrator, you can easily perform similar tests for your 4-20 mA vibration sensors.
The PVC is a NIST-traceable shaker that displays the known vibration input to a sensor. Your task is simply to record the known vibration levels displayed on the PVC and make note of the signal output from the 4-20 mA sensor. With this data and
tools provided with the PVC, you can easily determine the linearity of the sensor and create reports that can help your plant pass critical OSHA safety and insurance audits.
The following video demonstrates how to test an IMI Model 640B01 4-20 mA vibration transmitter using a Portable Vibration Calibrator from The Modal Shop.
Why test 4-20 mA loop-powered vibration transmitters? These sensors are rugged, but they can lose sensitivity over time. They may exhibit drift, failing to reach full-scale output. For example, when a velocity sensor whose maximum velocity is 1 in/s peak is driven to that maximum velocity, its output might have drifted from 20 mA to 18.7 mA, as shown in the certificate below:
If a sensor “fails” testing because it is not reaching full-scale output but is still exhibiting a linear response, the scaling in the PLC or DCS can be changed to adjust for this drift.
How to Test 4-20 mA Loop-Powered Vibration Sensors
With The Modal Shop’s Portable Vibration Calibrator and the optional 9100-PS02 Power Supply, a 4-20 mA sensor can be tested in the field. If the sensor is working as expected, there will be a linear relationship between vibration and output
current. Powering the sensor conveniently with a 9100-PS02 Power Supply plugged into the USB port on the Portable Vibration Calibrator, a known vibration can be applied by the PVC. The output of the sensor is read using a multimeter.
First, readings should be taken with no vibration. The vibration level should then be increased at a given frequency until vibration levels reach the top of the measurement range for the sensor under test. Output is often measured
at 25%, 50%, and 75% of the span of the sensor under test to confirm linearity throughout the sensor’s range. The PVC Report Generation Workbook, included with the purchase of a Portable Vibration Calibrator, can be used to create a linearity
certificate. Simply input the test data into the 4-20 mA Vibration Sensor table. If the response’s non-linearity is greater than 1% or if full scale output does not come within a certain percentage of what is specified (% of span), the
sensor fails calibration.
For more technical details on the calibration of 4-20 mA loop vibration transmitters, see this article: Expanding Your Process Calibrator Capability.
4-20 mA loop-powered vibration transmitters are critical components in the safety of your system. With the Portable Vibration Calibrator, you can have confidence that they are calibrated and working properly.
9100-PS02 Power Supply
- Convenient and portable, power is supplied for the calibration and testing of loop powered and modulated current sensors, via the USB drive on top of the shaker
- Internal precision resistor for accurate current and voltage measurements
- Works with the Modal Shop’s 9100D, 9110D, 9200D, and 9210D shakers
Test 4-20 mA Vibration Sensors
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- IMI Sensors: 640 Series 4-20 mA vibration transmitters and industry exclusive Smart Vibration Sensors such
as Reciprocating Machinery Protector
- Metrix: ST5484E and 162VTS Seismic Velocity 4-20 mA transmitter Hansford: HS-420, HS-421 4-20 mA velocity vibration transmitters and HS-422, HS-423 series 4-20 mA acceleration vibration transmitters
- Meggitt (Wilcoxon Research): PC 420 series 4-20 mA vibration sensors
- Robertshaw 570B and 571A 4-20 mA vibration transmitters
- Balmac: 140 series and 191 series two-wire vibration transmitters
- STI Vibration Monitoring: CMCP420VT and CMCP422VT series loop powered vibration transmitters