Level Sensor Outputs for Continuous Measurement
Selecting a level sensor or pressure transmitter, it’s vital to note that the output of the level sensor is always an important criterion. Outputs have more implications than whether or not they match the control system, though that is often the immediate need. Each has its pros and cons, and various reasons for use that should be understood, and considered carefully whenever there is a choice.
Without going into too much detail, the following is a list of outputs for continuous measurement with a brief overview of each:
- 4-20ma: Useful for long cable runs and when noise immunity is required. The 4-20mA transmitter signal works well for cable runs over 1000 ft. with almost no signal degradation. This output is great for most industrial applications and is very common.
- Amplified: Also called voltage output, it is used in short cable runs 100 ft. or less. It is often used in laboratory and electrically noisy environments. This output is compatible to most process systems.
- Non-amplified: Also called millivolt output, the signal conditioning is located remotely from the actual sensor. This keeps the sensor low cost and compact. This type of output is best for areas with low potential for electrical noise and with short cable runs.
- Fieldbus: Used for creating a network of control devices, fieldbus includes several competing protocols. Modbus is the most widely used of these. Fieldbus also reduces wiring costs and allows more data to be gathered.
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