USING TSI - Incorporated Micromanometers to Measure Pressure and Velocity - Application Note TSI-107 (A4)

Sep 27, 2026

Uploaded by noah

Guidance explains how TSI® micromanometers with pressure ports measure differential pressure, mapping the (+) port to higher pressure and the (−) port to lower pressure for correct positive or negative readings. The note clarifies that differential sensors cannot measure barometric pressure and then describes static pressure measurement using a static pressure tip or a pitot tube, and velocity pressure measurement with a pitot-static tube. It provides standard and actual velocity equations with units and conditions.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages4

Reading Time10 min

AccessFree to download

Differential Pressure Basics

Static Pressure Measurement Options

Velocity Pressure and Velocity Calculations

USING TSI® INCORPORATED MICROMANOMETERS TO MEASURE PRESSURE AND VELOCITY APPLICATION NOTE TSI-107 (A4) TSI® Incorporated meters with pressure ports measure differential pressure, or in other words, the pressure difference between the two pressure ports. The (+) port connects to the higher pressure and the (-) port connects to the lower pressure (often ambient pressure). Using these instruments to measure differential pressure is like using a digital voltmeter: when the pressure is connected the same way the tubes are marked, the meter displays a positive number. When the pressure is reversed, the meter displays a negative number. Although different terms are used to describe different types of pressure, all pressure can bethought of as differential pressure. For instance, the term “absolute pressure” refers to the difference between an absolute vacuum and the pressure of interest. The absolute pressure of ambient air is known as barometric pressure. | NOTE | | --- | | The differential pressure sensor cannot measure barometric pressure. If you try to measure barometric pressure (which is approximately 400 inches of water, or 101 kPa) by connecting the (-) port of the instrument to an absolute vacuum, the pressure sensor inside the unit will be destroyed because it is only designed to measure ±15 inches of water (3,735 kPa) . | Static pressure describes the difference between the pressure inside and outside a system, disregarding any motion in the system. For instance, when referring to an air duct, static pressure is the difference between the pressure inside and outside the duct, without taking into account pressure from any air flow inside the duct. Static pressure is often measured inside ducts in order to determine how hard the blower is working. A static pressure tip can be used for measuring static pressure. Attach the static pressure tip to a tube on the (+) port of the instrument. Keep the (-) port free so that it can measure ambient conditions. Make sure the static pressure tip is pointed directly into the airflow. If the static pressure in the duct is positive, the instrument will display a positive number. If the static pressure is negative, the instrument will display a negative number. The static pressure can also be measured using a regular pitot tube as shown in Figure 1, below. Apitot tube is a tube within a tube. The inside tube is open to the air at the tip of the tube (total pressure), and the outside tube is open on the sides of the tube (static pressure) . To measure static pressure with a pitot tube, you use only the static pressure port and ignore the total pressure port. Figure 1: Measuring static pressure with pitot tube The instrument can also be used for measuring velocity pressure (Velocity Pressure = Total pressure-Static Pressure) with a pitot tube and converting into air velocity. It is useful in locations where the thermal anemometer probe cannot be used. For instance, it may be desired to measure velocity in an exhaust stack, where high temperatures and high particle content could damage the velocity probe. Figure 2: Measuring velocity pressure with a pitot-static tube The front orifice of the pitot tube senses the total pressure, which is the static pressure in the duct plus the velocity pressure caused by air blowing into this orifice. By connecting the instrument to the pitot tube, you will get velocity pressure. When the measurement conditions are close to standard conditions of 70°F (21.1°C) and 14.7 psia (29.92 in. mercury or 101.4 kPa), the following equations can be used with a pitot-static tube to compute velocity: Vft/min = 4004.4~~ ~~P v Where: Vft/min = velocity in feet per minute Pv = velocity pressure measured by the instrument in inches of water Vm / s = 40.76Pv Where: Vm/s = velocity in meters per second Pv = velocity pressure measured by the instrument in kPa If the measurement conditions are substantially different from standard con

FAQs

How do the (+) and (−) pressure ports affect the micromanometer reading?

Connect the (+) port to the higher pressure and the (−) port to the lower pressure. With correct tube orientation markings, the meter displays a positive value, while reversing the pressure connections yields a negative value.

Why can’t the differential pressure sensor measure barometric pressure?

The sensor is designed only for a limited differential range (about ±15 inches of water). Attempting to measure barometric pressure by connecting the (−) port to an absolute vacuum can destroy the sensor.

What pitot-static method is used to compute velocity from measured pressures?

A pitot-static tube measures total pressure at the front orifice and static pressure through the side openings. The instrument provides velocity pressure, and the note supplies equations to convert velocity pressure into standard and actual air velocity under specified temperature and pressure conditions.

Sep 27, 2026

Uploaded by noah