Glossary of Terms
Laws of Thermodynamics
Heat energy can be changed in form and transferred between objects but cannot be created or destroyed. Heat energy flows from a hotter to a cooler body. Absolute zero can never be attained.
Limits of Error
The deviation in degrees or % of Standard or Special grade thermocouples in EMF outputs from an ideal calibration. This tolerance or calibration normally applies only from 0°C up to the maximum temperature for each thermocouple. Sub-zero limits require special calibrations.
In digital instruments, a numerical readout in which the digit segments are delineated by dark areas in a liquid-crystal display.
Lead Length Consideration
Connecting leads can affect the accuracy of small current transformers, DC shunts and low voltage analog voltmeters. Use leads supplied with device or lead size specified.
In digital instruments, a numerical readout in which the digit segments are delineated by light-emitting diodes.
A measure of the departure from a straight-line response in the relationship between two quantities, where the change in one quantity is directly proportional to a change in the other quantity. Usually expressed as a maximum percent. Rotational displacement in analog meters, particularly for low-level measurements and/or AC parameters, is distinctly non-linear with respect to changes in the quantity under measurements; accuracy in these cases is maintained by means of properly calibrated non-linear scale cards.
The electrical resistance, in ohms, of a complete thermocouple circuit exclusive of an instrument’s internal resistance.
Least-Significant Digit (LSD)
The rightmost active (non-dummy) digit of the display.
For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5V, which can source 20 µA, and a logic 0 is obtained for inputs of 0 to 0.8V which can sink 400 µA. For digital output signals, a logic 1 is represented by 2.4 to 5.5V with a current source capability of at least 400 µA; and a continued - logic 0 is represented by 0 to 0.6V with a current sink capability of at least 16 mA. “LS” stands for low-power Schottky.
LS-TTL Unit Load
A load with LS-TTL voltage levels, which will draw 20 µA for a logic 1 and -400 µA for a logic 0.