Sensors, Transducers, and Signal Transmission in Process Control

Need for Sensors, Transducers, and Signal Conditioners

Devices like sensors, transducers, and signal conditioners are essential for maintaining precise and consistent control over any process, minimizing potential errors.

Serial vs. Parallel Data Transmission

Serial data transmission can be faster than parallel transmission at high speeds. In parallel transmission, induced voltages between lines at high speeds can attenuate the signal, reducing its effectiveness.

Incremental vs. Absolute Encoders

Advantages of Incremental Encoders

• Manipulating the resolution is easier than with absolute encoders, which have fixed resolutions.

Disadvantages of Incremental Encoders

• Determining the absolute position without recalibration is challenging if the system loses power or experiences an interruption.

Incremental encoders function by counting pulses from a rotating drum to determine angular position.

Determining Linear Displacement Direction with Incremental Encoders

By adding a second sensor at a known distance from the first, the direction of linear displacement can be determined. The sensor that detects the signal first indicates the direction of movement.

Thermocouples

Thermocouples are self-powered temperature sensors with fast response times. They operate based on the Seebeck effect, which generates a voltage between two dissimilar semiconductors at different temperatures. Typical operating ranges are -200°C to 1600°C and 0°C to 1500°C. Conditioning circuits for thermocouples must not interfere with the thermocouple's reference junction and should be isolated to prevent measurement errors.

Uncertainty Error

Uncertainty error in digital-to-analog conversion depends on the converter's conversion time and the rate of change of the analog signal.

Trapezoidal Integration

Integration using the trapezoidal method provides a good approximation. This method, known as bilinear transformation, is employed when a discrete controller needs a frequency response similar to its analog counterpart.

Sampling and Quantization

Sampling involves obtaining discrete values of a continuous signal at intervals of Ts (sampling period). Quantization assigns a digital code value to each sampled value.