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HA249928
Issue 15 Jly 06
100 MM CHART RECORDER USER GUIDE
Trace
The line produced on the chart or display screen showing the value of the process variable
being measured.
Thermocouple
A junction of two dissimilar metals which produces a small voltage, the value of which de-
pends on the temperature of the junction. The voltage varies in a non-linear way with tem-
perature, but for any given type, this non-linearity is well known and invariable and is
compensated for by linearisation tables in the recorder memory.
Threshold
See setpoint.
Transducer
A device which produces an electrical output proportional to temperature, flow rate, pres-
sure, speed, position etc. Common transducers are potentiometers, thermocouples, resistance
thermometers (RTDs) and flow meters.
Transmitter
Thermocouple wire (compensation wire) is expensive, and if the thermocouple is a long
way from the measuring device, it is often cheaper to instal a ‘transmitter’ local to the ther-
mocouple. This device converts the mV signal from the thermocouple to a mA signal which
can then be wired to the recorder using normal copper wire. Transmitters can be self pow-
ered, or they may need power generated for them. Most recorders can be fitted with Trans-
mitter Power Supplies as an option.
Writing system
A general term used to describe the mechanical means of moving pens/printheads across the
chart width. The term often includes the paper transport system used to drive the chart
through the cassette.
Zero
Zero is generally taken to mean the value associated with the left-most grid line on the chart.
Its actual value need not be zero, as long as it is less than the Span value.
