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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.
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- 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.
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- Hardwired
- Physically interconnected and intended for a specific purpose. Hardwired
logic is essentially unalterable.
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- Hazardous Location
- Defined as an area in which flammable or combustible mixtures are present.
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- Head-On
- Condition whereby the target approaches the sensing face of the proximity
sensor with its center along the sensing face.
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- 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.
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- Hermetically Sealed Switch
- Switch completely sealed to provide constant operating characteristics. All
junctures made with metal-to-metal or glass-to-metal fusion.
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- Hertz (Hz)
- Unit of frequency equal to one cycle per second.
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- Hexadecimal
- Counting system based on 16.
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- High Contamination
- Heavy particle laden air, extreme washdown environments, grain elevators.
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- High Limit
- Control shuts down a system if a condition exceeds its maximum value for
safe operation.
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- High Output Limit
- highest value of output beyond which controller automatic output cannot
exceed.
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- 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.
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- High Reset Limit
- Highest value of output beyond which no reset should occur.
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- 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.
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- Highway Addressable Remote Terminal (HART)
- Provides digital communication to microprocessor-based (smart) analog
process control instruments.
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- Horsepower
- 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.
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- 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.
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- Humidity
- 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.
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- Hysteresis
- 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.
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- 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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