Glossary of Terms - H


Current or voltages which have frequencies that are integer multiples of the fundamental power frequency; common and sometimes dangerous in nonlinear loads.


Thermal energy, attributable to molecular activity. Energy can be changed in form (first law of thermodynamics) so energy can be expressed in either mechanical work units (Joules or ergs) or thermal energy units (calories or BTUs).

Heat Transfer

Conduction: By contact within the same body or from one body to another. Body can be solid, liquid or gas. In metals, conductance occurs by the movement of valence electrons.

Convection: Heat transfer by actual motion of the hot material (liquid or gas).

Radiation: Heat transfer via transforming thermal energy into electromagnetic waves that travels through space (air or vacuum). The wave is retransformed into heat upon absorption by receptor.

Heat Treating

A method of thermal strain relieving T/C or RTD wires that have been cold-worked (stamped, machine-formed, etc). For Platinum RTDs elements after winding, anneal at 1800-2200°F, then air-cool. For thermocouples, anneal for 15 minutes at 900-1000°C, cool slowly at about 500°C, then air-cool. Heat treat in clean dry air or Nitrogen or Argon or (if components are required bright) in cracked ammonia or hydrogen with a very low dew point (-40°C and low impurity content). Before annealing, decrease in TCE or other suitable solvent.

Heating Effect

Temperature increase in electrical distribution equipment caused by an increase in RMS current.


Meter HOLD is an external input which is used to stop the A/D process and freeze the display. BCD HOLD is an external input used to freeze the BCD output while allowing the A/D process to continue operation.


An error resulting from the inability of an electrical signal or mechanical system to produce the same reading or position when approached slowly from either direction. Also referred to as dead band.


Frequency in cycles per second, pulses per second, events per second, etc.

60Hz Rejection

The insensitivity of an amplifier to an interfering signal usually expressed in dB. Twenty dB means 10 times, 40 dB means 100 times, 60 dB means 1000 times, etc. The 60Hz rejection specification means that an interfering 60Hz signal 100 times higher (40dB) than the full-scale sensitivity of .1 volt will not cause an error.