BASIC CONCEPTS OF INDUSTRIAL INSTRUMENTATION

What is instrumentation?
In all processes, it is absolutely necessary to control and keep constant some quantities, such as pressure, flow, level, temperature, pH, conductivity, speed, humidity, etc. The measurement and control instruments allow the maintenance and regulation of these constants in more suitable conditions than those that the operator himself could perform. In short, the instrumentation is in charge of keeping the process running optimally through elements that serve to measure, convert, transmit, control or register the variables.

instrumentation

In the previous image, we can see some of the main components of the instrumentation

Transmitter: used to receive the signal from the sensor and convert it to a standard 4-20ma
Registrar: as its name indicates, it registers the status of the process
Controller output: Controls the output signal, to send it to the actuator, keeping the variable to be controlled as close as possible to the set point.
What concepts should I understand to get started with instrumentation?
Sensor: We call a device a sensor that automatically measures a variable, such as a temperature, pressure or even the rate of rotation, among other things.

sensor

Transmitter: The signal conditioning unit is known as a transmitter in the field of instrumentation and control.

transmitter

Transducer: It is the instrument or device capable of transforming the available energy in a given physical magnitude into another magnitude. They are used, for example, to go from conditioned quantities in pressure to current or voltage and, in modern times, to digital variables for field buses.

Range: It is the set of values between the limits (Upper and Lower) that is capable of measuring the instrument to which we refer.

instrumentation range

Resolution: It is the smallest change in the process variable capable of producing a noticeable output on the instrument.

Error: It is defined as the difference between the measured value and the true value.

sensor error

Accuracy: Ability of an instrument to give small error values.

Accuracy: The higher the precision, the smaller the dispersion of the measurement values around the measured value.

Repeatability: The ability of an instrument to repeat the output when the measurement is reached repeatedly under exactly the same conditions.

Hysteresis: it is the capacity of an instrument to repeat the output when it reaches the measurement on consecutive occasions under the same general conditions but once with the measurement of the variable in one direction (for example increasing) and in the next with a variable in the direction contrary (for example decreasing).

hysteresis

Interchangeability: When referring to the interchangeability of instruments, several aspects can appear. Regarding accuracy, if an instrument of 1% is replaced by another with the same accuracy, given that errors can be added under certain conditions when making the change we will say that we can ensure the measurement at 2 % if we do not take special calibration precautions.

Calibration: Calibration is the process of comparing the values obtained by a measuring instrument with the corresponding measurement of a reference (or standard) standard.

Sensitivity: It is the variation in the output of the instrument per unit of variation of the process variable (input), in short, it can be said that it is the gain of the instrument.

Zero error: Even when the value of the process variable is at the minimum of the range, where the output of the instrument must be the value associated with the zero of the range (in current, for example, 4mA), the instrument marks a value at its output non-zero.

zero error

Linearity: It expresses how constant the sensitivity of the sensor or measuring device is. Constant sensitivity (high linearity) makes it easy to convert the read value to the measured value.linearity

Stability: ability to keep its transfer curve unchanged for long periods of time.

Active – Passive Transducer: A transducer that is passive when it is not powered from any source other than the same process it is measuring.
On the other hand, the asset is the one that generally needs less energy from the process to be measured, since it has an external source for its operation.

Desired inputs: these are the inputs to the measurement system of the physical variables that we want to measure.

Interferences: These are unwanted inputs that the instrument detects without the intention of doing so.

Modifying inputs and disturbances: They are those that cause variations in the desired inputs as well as interference

Rangeability: It is the relation between the maximum value of the measured variable with respect to the minimum over which the specified accuracy of the instrument will be maintained.