MULTIPOINT CIRCULAR-CHART RECORDER INSTALLATION AND OPERATION MANUAL
Section 5
Page 5 - 7
HA250385
Issue 2 Mar 98
5.4 GLOSSARY OF TERMS
The following glossary is general to all the manufacturer’s products and may thus contain terms which are not appli-
cable to your particular unit. In particular, many of the terms are relevant only to configurable recorders.
Alarm
A function which is triggered when an input signal or a signal derived from it reaches a
certain value (absolute or deviation alarms) or changes faster than a specified rate (rate-of-
change alarms) or changes state (digital alarms). Once triggered, the alarm can initiate a
job list, such as causing a relay output to change state, sounding a buzzer, changing chart
speed etc.
Analogue input
An input which changes in a smooth (non-stepped) way (e.g. thermocouples, resistance
thermometers).
Analogue output
An output from the recorder which is a scaled and linearized copy of an analogue input or
derived channel. Also called retransmission output.
Attenuator
A resistive device which reduces the signal voltage by a known ratio (usually 100:1)
Break response
The recorder can detect an open circuit at its input terminals. As a part of the channel con-
figuration, the instrument’s response to an open circuit can be defined as ‘None’, ‘Drive
high’ or ‘Drive low’. If ‘none’ is selected the trace is allowed to drift according to what the
input wiring is picking up (acting as an aerial). Drive high (low) causes the trace to be
drawn at the extreme right (left) side of the chart.
Chart drive
A mechanical paper rotation. Includes chart hold-down tabs and a means for gripping the
center of the chart to turn in at a specified rate..
Cold Junction Compensation
Also known by the abbreviation CJC. The current generated by a thermocouple (TC) junc-
tion depends on the temperature difference between the actual bonded junction (the hot
junction), and the other (non-bonded) end of the conductors (the cold junction (CJ)). Thus,
for any reading from a TC to be accurate, the temperature of the CJ must be taken into
account. This can be done in three ways: Internal, External or Remote.
Internal. The recorder has integral temperature detectors measuring the temperature near
the terminal blocks (the cold junction for directly connected TCs).
External. For remote TCs, the cold junction can be held at a known temperature. This tem-
perature is entered (in degrees) as a part of the CJC configuration.
Remote. For remote TCs, an auxiliary temperature detector can be used to measure the
cold junction temperature. This detector is then connected to a separate input channel. This
input channel number is entered as a part of the CJC configuration.
Communications
Most recorders now offer a ‘Serial Communications’ option to allow a computer (PC) to
communicate directly with one or more recorders in order to configure them, or to read
information from them regarding the process variables being measured.
Configuration
This is used as a verb to mean ‘the process of telling your recorder what you want it to do’,
and as a noun to mean ‘the way in which the recorder has been set up (or configured)’. Re-
corders fitted with memory card or communications options can save their configuration to
the memory card or to the host computer. This ensures against loss, and also allows con-
figurations to be copied from one recorder to another.
Counters
Counters can be incremented or decremented by digital/discrete inputs or by job list action.
Counters can be preset. Each counter can have a set point which triggers a job list when
the counter value passes through the set point either incrementing (High) or decrementing
(Low).
Data acquisition
A general term describing the successful reading of an input signal. The term Data Acquisi-
tion Unit describes those units which are able to read input signals and act upon them
(alarms retransmission maths functions etc) without necessarily having the facility of dis-
playing or recording them.