Understanding Differential Pressure Measurement: Differential Pressure Gauge Example

This video (courtesy of Ashcroft) does an outstanding job illustrating the concepts of differential pressure and flow measurement using the differential pressure method.

Engineered restriction devices are often inserted into a closed pipe system to create a differential pressure for the purposes of measuring fluid flow rate. These restrictions can come in the form of an orifice plates, Venturi, wedge, and other designs.

To measure the differential pressure, taps must be installed on both sides of the plate.  The upstream side will always produce the greater pressure, and is referred to as the high side. Conversely, the downstream pressure will always be the lesser value, due to the obstruction.

A differential pressure gauge's range is based on the maximum difference that can be expected as a result of the restriction. The gauge's dial will display the differential pressure in units of pressure measurement, like psi or bar.  By applying the linear square root relationship between flow rate and pressure, the gauge style can be scaled in a specified rate of flow, such as gallons per minute. A dual scale dial can also be created to display both the flow rate and the differential pressure.

Another important consideration is the maximum line pressure, also referred to as the static pressure. The higher the static pressure, the more robust the gauge must be to contain it. That's why it's crucial to ensure that the gauge carries a static pressure rating that exceeds the highest pressure in the line.

For more information about differential pressure gauges, transmitters, and flow measurement, contact Mead O'Brien at (800) 892-2769 or visit their web site at https://meadobrien.com.

Two Point Calibration of the Foxboro IDP-10-T Pressure Transmitter

The Foxboro / Schneider Electric I/A Series Electronic Pressure Transmitters are a complete family of D/P Cell, gauge, absolute, multirange, multivariable, and premium performance transmitters, as well as transmitters with remote or direct connect seals, all using field-proven silicon strain gauge sensors and common topworks.

A common HART electronics module is used for all HART Pressure Transmitters. Also, because all configuration and calibration data is stored in the sensor, you can replace a HART module with another HART module without transmitter reconfiguration or recalibration.

The video below provides step-by-step instructions for two point calibration of the IDP-10-T pressure transmitter.

Understanding Differential Pressure or Delta-P

Differential pressure or Delta-P

Commonly, filters and strainers are positioned to capture solids and particulate. The filter will obstruct the flow through the pipe lowering the pressure on the downstream side. These effects may vary depending on the filters construction. Filter media is the material that removes impurities. The smaller the pores the larger the friction. Higher friction means greater pressure drop. Contaminants for particulates that buildup in the filter will reduce media flow. As the filter becomes clogged the downstream pressure drops. This results in an increased differential pressure, also referred to as the Delta-P. Saturated filters may also begin to shed captured particles.

With the filter no longer functioning properly, the contaminants can escape into the process. This is why proper monitoring of pressure drop is crucial. So how can we measure the DP? Placing taps both before and after the filter, a differential pressure measuring instrument can be connected to detect the high side and close side pressures. the instrument will report the difference between the two sides. The saturation point will be indicated when the Delta-P value reaches a predetermined threshold. This value is derived from a calculation that factors in the flow rate, fluid viscosity, and filter characteristics.

When specifying a differential pressure instrument there are two important factors to consider. The first is the DP range, which is based upon the most difference in pressure that the restriction is likely to produce. The second is the instruments ability to contain the line or static pressure level.

For more information on pressure measurement, call Mead O-Brien at (800) 892-2769 or visit www.meadobrien.com.

Here is a great video, courtesy of Ashcroft, that provides an excellent visual understanding of differential pressure.