A-4 Technical Instruments and Testers Introduction
Commissioning equipment requires the use of various sensors and instruments. Often, one piece of equipment may require the use of multiple instruments to ensure proper and safe operation.
Learning Objectives
After completing the learning tasks in this competency, you will be able to:
- Describe pressure and temperature-measuring tools.
- Interpret pressure readings.
- Use U-tube and digital manometers.
- Use temperature-measuring instruments.
- Use electrical testing meters to test voltage, amperage, resistance and continuity.
- Use combustible gas indicators.
Terminology
The following terms will be used throughout this section. A complete list of terms for this section can be found in the Glossary.
- absolute pressure: When the pressure is relative to a perfect vacuum, it is referred to as “absolute pressure,” which equals gauge pressure plus atmospheric pressure. (Section A-4.1)
- differential pressure gauge: A type of gauge with two inlet ports, each connected to one of the volumes whose pressure is to be monitored; this gauge can be used to monitor air flow, check the amount of filter clogging, and test equipment operation; it performs the mathematical operation of subtraction through mechanical means. (Section A-4.1)
- digital instruments: Instruments that use electronics to read and display exact numerical data or measurements using LEDs or LCDs as numbers on a screen, like a calculator; easier to read than analogue instruments since you don’t have to interpret the numbers on a scale. (Section A-4.3)
- digital manometer: The most common portable field pressure-measuring tool due to its many advantages over traditional instruments; it uses micro-pressure sensors that alter electrical resistance when pressure is applied and can measure positive, negative, or differential pressures; this tool is compact, can be used in any position, and does not require fluid. (Section A-4.1)
- distance-to-spot ratio (D:S): A ratio that tells you how far you need to be from an object to measure its temperature accurately with a thermometer; a higher D:S ratio means you can measure temperature from farther away, like using a zoom on a camera to focus on something far off. (Section A-4.2)
- emissivity: A number from 0 to 1 that indicates how much heat a material lets out as radiation; 1 means it gives off radiation well, like a perfect black object; lower numbers mean less heat is released. This matters in infrared thermometers, where knowing emissivity helps get accurate temperature readings by adjusting for how materials reflect or emit heat. (Section A-4.2)
- infrared (IR) thermometer: An Instrument that measures temperature by detecting thermal radiation emitted by the object being measured, often referred to as black-body radiation; also known as a laser thermometer due to use of a laser for aiming, or as a non-contact thermometer or temperature gun because it can measure temperature from a distance; by assessing the amount of infrared energy emitted and considering emissivity, infrared thermometers can estimate the object’s temperature within a specified range; belongs to the category of devices known as “thermal radiation thermometers.” (Section A-4.2)
- ohmmeter: A tool used to measure how much something resists the flow of electricity (electrical resistance); it tells you the resistance in units called ohms (Ω); multimeters can serve as ohmmeters when set to resistance-measuring mode; to measure resistance, an ohmmeter applies a current to the circuit or component under test. (Section A-4.2 and Section A-4.3)
- Positive temperature coefficient (PTC) thermistors: Resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature; they are made from materials such as silicon or barium titanate, known for their high resistance properties, and they have various uses such as temperature sensors, self-regulating heaters, and resettable fuses. (Section A-4.2)
- pressure measurement: The analysis of an applied force by a fluid (liquid or gas) on a surface; pressure is measured in units of force per unit of surface area. (Section A-4.1)
- RTD thermometer: A device that measures temperature by detecting changes in electrical resistance; RTDs can have a range of –200°C to +500°C. (Section A-4.2)
- thermocouple: Also referred to as a “thermoelectrical thermometer,” an electrical device composed of two different electrical conductors that form an electrical junction; through the Seebeck effect, generates a voltage that varies with temperature, allowing for temperature measurement; extensively used as temperature sensors. (Section A-4.2)
- water column (WC): A method for measuring pressure, defined as the pressure produced by a 1-inch by 1-inch column of water of a specified height; useful for expressing low pressures, such as describing 0.072 psi as 2 inches of water. (Section A-4.1)
