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Appendix A Glossary
Page A.4
H
Hazardous area
An area where there is a risk of fire or explosion.
Health check
A check that all inputs and devices connected to the 7951 are operating
normally.
Hg
The chemical symbol for the element Mercury.
Historical log
A log of every alarm received by the 7951.
Hub
A common connection point for devices in a network. Hubs are
commonly used to connect segments of a LAN. A hub contains multiple
ports. When a packet arrives at one port, it is copied to the other ports
so that all segments of the LAN can see all packets.
A passive hub serves simply as a conduit for the data, enabling it to go
from one device (or segment) to another. So-called intelligent hubs
include additional features that enables an administrator to monitor the
traffic passing through the hub and to configure each port in the hub.
Intelligent hubs are also called manageable hubs.
I
Instrumentation earth
In a large installation where the instrumentation and chassis are
earthed separately, this is the “clean” earth to which the instrumentation
is connected.
Interrogate
To ask another part of a system to supply information.
J
J
See Joule.
Joule
The unit of work. 1J = 1N/m
2
.
Jumper
A metal bridge that closes an electrical circuit. Typically, a jumper
consists of a plastic plug that fits over a pair of protruding pins. Jumpers
are sometimes used to configure add-on (option) boards. By placing a
jumper plug over a different set of pins, you can change a board's
parameters.
K
K-factor
The K-factor relates the output from a flow meter to a specific set of
units. For volume output meters such as turbines, it is often quoted as
pulses per meter cubed.
Kinematic viscosity
The ratio of the dynamic viscosity of a fluid to its density.