Sensor transmitters are signal conditioning or measurement packages that offer a standard and calibrated output from transducers and sensors. The output types of sensor transmitters include variable voltage levels, pulse or frequency signals, current loops, counters or timers, variable resistance outputs and relays.
The sensor transmitters can also offer transistor-transistor logic (TTL) and radio frequency (RF) signals output. Current loop like 4 – 20 mA are ideal for sensing signals over long distances. The current imposed on the output circuit is usually proportional to its measurement. Feedback is also used for offering an appropriate current, irrespective of the impedance and its line noise.
Modulated frequency or frequency output of sensor transmitters include;
• Pulse trains
• Sine waves
• Frequency modulation (FM)
• Amplitude modulation (AM)
Types of input received by sensor transmitters
The sensor transmitters can receive three types of input; sensor inputs, signal inputs and from special devices. The signal inputs of sensor transmitters include AC current, DC current, AC voltage and DC voltage. They also include charge and frequency signals that require amplification and filtering.
Sensor transmitters can also receive inputs from thermocouples, resistance temperature detectors (RTD), accelerometers and thermistors. Strain gauges are another means through which sensor transmitters can receive input. Most strain gauges utilise a Wheatstone bridge from both rotary and linear variable differential transformers (RVDT and LVDT).
Signal inputs from special devices include encoders and signal per cycle counts from tachometers and counters. Switches, relays, clocks, timers can also provide special inputs to these sensor transmitters.
