Engineering Notes on Pressure Measurement
What are the effects of water hammer and pulsation? - Pressure spikes created by quickly closing valves, positive displacement pumps and vertical pipe runs can have damaging effects.
How do you measure pressure with weights? - The first pressure measurements were made using columns of fluid, and the technique is still in use today.
How is pressure related to altitude and depth? - The typical altimeter (and/or depth gauge) is a pressure measuring instrument that calculates its altitude (or depth) according to the local air or water pressure.
What is air pressure? - The mass of air at standard gravity creates an ambient atmospheric pressure of approximately 1000 millibar at sea level.
What is a pressure gauge siphon? - A pressure gauge siphon is a simple device used to protect a pressure sensor from high-temperature media, such as steam.
What governs the output from a 0-xV amplified pressure transmitter? - There are a number of pressure transmitters on the market with built-in amplifiers that provide 0V output at zero pressure.
What is the output of a current loop pressure transmitter? - The output from a current loop pressure transmitter is independent of supply voltage.
What is the output from a pressure sensor with an inbuilt amplifier? - The output from a pressure sensor with an inbuilt amplifier is normally independent of the supply voltage.
What governs the output of a pressure sensor? - The output from a Wheatstone bridge depends on the excitation voltage and is normally specified as a millivolt output per excitation voltage.
What is a flush diaphragm pressure sensor? - Flush diaphragm pressure sensors are widely used in the food and chemical industries to avoid dead pockets in machinery and to facilitate cleaning to remove all germs and bacteria.
How do you choose an O-ring? - When installing a pressure sensor it is important to choose the right sealing gasket to give long-life performance.
How do you measure liquid level using the bubble principle? - Liquid levels can be measured by mounting a pressure sensor on the discharge side of a high-reliability pump: the pressure required to bubble air through an immersed pipe is directly related to the liquid level.
How do you avoid noise in sensor cables? - Noise is a form of electromagnetic energy picked up by transmission conductors. It is particularly troublesome in long wires that act as antennas.
What is an instrumentation amplifier? - The instrumentation amplifier or differential input amplifier is one of the most versatile signal processing components available.
How do you ensure corrosion resistance? - As many pressure sensors are manufactured either fully or partly from stainless steel, it is advisable to consult a corrosion resistance data list.
Why is response time important? - The response time of a pressure sensor is much faster than that of a pressure gauge. Indeed, in some cases pressure sensors can be too fast to be followed by standard electronics.
What is the thermal effect on span? - A change in the temperature of a pressure sensor will cause a change in the slope of the sensor output curve.
What is the thermal effect on zero? - Changes to the temperature of a pressure sensor will cause the entire output curve to move up or down along the output axis.
What's the problem with shock and vibration? - Shock and vibration are among the worst enemies of any pressure sensor.
What is interchangeability? - True interchangeability between pressure sensors requires that the signal output of each sensor is preset to give the same output at zero pressure and the same span at full scale.
Why worry about ageing? - Even though sensors are designed to operate within the elastic area of the material used and theoretically have infinite lifetimes, all sensors exhibit some level of “drift” (or deregulation) with time.
What is ratiometric output? - The span output of an unamplified pressure sensor is essentially ratiometric (or proportional) to the excitation voltage applied.
What defines resolution? - Most sensors give an analogue signal output, which in theory has an infinite or limitless resolution. The resolution itself is derived from the electronic equipment that measures the signal from the sensor.
What is repeatability? - The repeatability error of a pressure sensor defines how good the electrical output is for the same pressure input if tried again and again under the same conditions.
What are hysteresis errors? - The hysteresis error of a pressure sensor is the maximum difference in output at any measurement value within the sensor's specified range when approaching the point first with increasing and then with decreasing pressure.
Linearity or nonlinearity? - Linearity error is the deviation of the sensor output curve from a specified straight line over a desired pressure range.
What is the effect of null offset on full-scale output? - The null offset of a pressure sensor is the electrical output present when the pressure on both sides of the diaphragm is equal.
What is a 4-20mA current loop? - One of the amplified sensors commonly used is the two-wire 4-20mA or 10-50mA system.
What technologies are used in pressure sensor design? - There are a number of different technologies that can be used in the design of pressure sensors.
Pressure element or pressure sensor – what's the difference? - What exactly is a pressure sensor? This note looks at the key components used to measure pressure.
How will the sensor interface mechanically? - There are many ways to bring pressure to a sensor but, as always, there are several questions that must be answered before choosing.
What pressure will the sensor measure? - Working out the exact pressure profile of any piece of equipment is no trivial matter.
What's the fuss about media compatibility? - When choosing a pressure sensor for any application it is essential that the complete sensor is compatible with the media it will be used to measure.
How do you select a sensor? - Selecting the correct sensor for any given application, regardless of whether it is a pressure sensor, temperature sensor or load cell, requires answers to a number of questions.
How can you protect sensors against high-temperature media? - The expense of a special device can often be avoided if the sensor is isolated from the pressure source by a short length of pipe or tubing.
How does temperature affect pressure sensors? - All pressure sensors are subject to errors caused by temperature variations, and these must be considered in sensor selection.
What determines the accuracy of a pressure sensor? - The total error contribution is a crucial measure of the accuracy of any pressure sensor.
How frequently do sensors need calibration? - The recalibration period for a pressure sensor depends on several factors, ranging from the accuracy required to the environment of the application.
Overpressure – can you take it? - The overpressure possible in the application is a key factor to consider when selecting the correct pressure range for a sensor
What are the different types of pressure measurement? - Gauge, sealed, absolute and differential: a quick look at the differences between pressure sensors.