What is hysteresis in an instrumentation system, and how does it affect accuracy?

Hysteresis is a phenomenon that occurs in an instrumentation system when the output of the system does not immediately respond to a change in input. In other words, the output of the system depends not only on the current input value but also on the previous input values.

Pressure sensing is one of several physical systems that frequently experience hysteresis. It refers of the lag or delay in a physical response to modifications in the forces or circumstances around. In the case of pressure sensing, hysteresis may prevent the diaphragm from returning to its initial position right away following a change in pressure. This may affect the sensor’s overall functioning and lead to inaccurate readings from the sensor. Understanding hysteresis and how it affects sensor performance is essential for maximizing pressure sensing accuracy. Pressure sensing mistakes can be minimized or fixed by using the right methodologies and calibration processes after determining the causes and features of hysteresis.

The changes in a pressure transmitter’s output in response to pressure fluctuations are depicted in the figure by a hysteresis loop. The diaphragm deflects when pressure is applied to the transmitter’s pressure sensor(diaphragm), increasing the current output. The transmitter’s output is delayed because the diaphragm does not instantly return to its resting position when pressure is released. Hysteresis is a delay that might result in inaccurate readings from the transmitter, impairing its overall effectiveness. In order to understand its causes, features, and calibration processes and to correct for or reduce output errors in the instrument, it is essential to comprehend hysteresis in pressure sensing.

The accuracy of the sensor depends on the diaphragm’s integrity of the pressure transmitter. The hysteresis of an item depends on its material; if the diaphragm is constructed of lower-quality components, its accuracy could shift significantly over time.

High precision pressure transducers are necessary for the majority of test and measurement applications in order to function properly and safely. To maintain their strength and structural integrity, stainless steel diaphragms used in sensors for these applications need to be heat-treated.

For example, suppose you are measuring the pressure in a hydraulic system, and the pressure is gradually increasing from 0 to 100 psi. If there is hysteresis in the pressure sensor, the pressure reading may be slightly higher than the actual pressure as the pressure is increasing. On the other hand, if you then decrease the pressure from 100 psi back to 0 psi, the pressure reading may be slightly lower than the actual pressure as the pressure is decreasing.

In this way, hysteresis can cause a difference between the actual pressure and the measured pressure, which can lead to inaccurate measurements. To reduce the effect of hysteresis on accuracy, it is important to choose a pressure sensor that has a low hysteresis specification and to calibrate the sensor regularly to ensure accurate readings.