Glossary of Terms: H

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Hall Effect Technology
Description given to the following phenomena; when a semiconductor through which a current is flowing, is placed in a magnetic field, a difference in potential (voltage) is generated between the two opposed edges of the conductor in the direction mutually perpendicular to both the field and the conductor. Typically used in sensing magnetic fields.
Hardware Trigger
A trigger is something that causes a data acquisition system to start collecting data. When not generated by software it is known as a hardware or external trigger.
Physically interconnected and intended for a specific purpose. Hardwired logic is essentially unalterable.
Hazardous Location
Defined as an area in which flammable or combustible mixtures are present.
Condition whereby the target approaches the sensing face of the proximity sensor with its center along the sensing face.
Heat Sink
Any object that conducts and dissipates heat away from an object in contact with it. Also a finned piece of metal, usually aluminum, that is used to dissipate heat generated by electrical and electronic devices.
Hermetically Sealed Switch
Switch completely sealed to provide constant operating characteristics. All junctures made with metal-to-metal or glass-to-metal fusion.
Hertz (Hz)
Unit of frequency equal to one cycle per second.
Counting system based on 16.
High Contamination
Heavy particle laden air, extreme washdown environments, grain elevators.
High Limit
Control shuts down a system if a condition exceeds its maximum value for safe operation.
High Output Limit
highest value of output beyond which controller automatic output cannot exceed.
High Pass Filter
When a low-level transducer signal is superimposed on a large DC output voltage, a high-pass filter might be useful. This attenuates (removes) low frequencies. Using a cut-off frequency of, say, 4 Hz, will eliminate the DC voltage which has a frequency of zero. A high-pass filter will remove Drift.
High Reset Limit
Highest value of output beyond which no reset should occur.
High Temperature Sensor
High temperature sensors usually consist of two parts: a high temperature probe and an inline electronic amplifier. Both are linked with a Teflon cable. Advantages: reliable detection up to 180°C.
Highway Addressable Remote Terminal (HART)
Provides digital communication to microprocessor-based (smart) analog process control instruments.
Unit of measure (per James Watt), one horsepower, shows how much work mine ponies could do in an hour lifting coal out of the mine. One horsepower is equal to 746 watts.
Human machine interface (HMI)
The communication device between the computer system and the people who use it. Usually includes a display and some form of keypad or touchscreen for interaction. AKA man machine interface.
A relative humidity up to 90 % has nominal effect on the sensing distance of the sonic sensors. Direct moisture or dirt however may lead to a reduction of the scanning range Sd.
A band of change in process variable around the setpoint required to re-energize the control or alarm output. The signal change before the output unit (valve or similar) moves. Adjustable overlap of On/Off states of each control output or alarm.
Hysteresis, Switching
The principle associated with sensors, such that the operate point is not at the same level as the release point. In solid state sensors, it is accomplished electrically. In mechanical switches, it results from the storing of potential energy before the transition occurs. Also known as differential, and is usually expressed as a percentage of the operate point (e.g. 3-15%).
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