MULTIPOINT CIRCULAR-CHART RECORDER INSTALLATION AND OPERATION MANUAL
Section 5
Page 5 - 9
HA250385
Issue 2 Mar 98
Constant
Square root
Log base 10
Latching maximum
Switch
Copy
Channel average
Rate of change
Continuous maximum
High select
Add
Group average
Sample and hold
Polynomial
Low select
Subtract
Rolling average
Channel minimum
Relative humidity
Trace generator
Multiply
Exponent
Latching minimum
Linear mass flow
Stopwatch
Divide
Natural log
Continuous minimum
Square root mass flow
Time stamp
Modulus 10x
Channel maximum
Zirconia probe
F value
Maths functions (Cont.)
Measured value
An umbrella term which means: the value of an input channel, derived channel, totaliser,
counter, timer etc. measured in mathematical units as a proportion of the span. See also
Process variable.
Memory card
Used to describe SRAM (Static Random Access Memory) solid state memory cards, or
portable hard or floppy disks, used to record configurations, data etc. which can then be
taken to a remote PC for further analysis, if required.
Multipoint recorder
This is used to describe recorders which have multiple pen printheads rather than individual
pens to produce the trace on the chart. Each trace is made up of dots, produced by the
printhead as it traverses across the chart at regular intervals. Advantages are that many
more traces can be laid down on the chart, the traces can be annotated for identification and
messages can be printed on the chart. Disadvantages are that fast transients may be missed
at low chart speeds.
Operator interface
A term used to describe the controls (e.g. pushbuttons, keypads) and visual feedback (dis-
play) that are used to operate and configure the unit.
Paper transport system
This includes the chart cassette and the mechanical system, motors etc. needed to move the
chart through the cassette. The paper transport system is often considered to be an integral
part of the writing system.
Pen
A fiber-tipped disposable stylus with an integral ink reservoir. Used to draw (trace) the
value of a single process variable on the chart in continuous trace recorders.
Printhead
This is a device which, together with a disposable multi-colour cartridge, allows multi-
point recorders to mark the chart.
Process variable
An umbrella term which means: the value of an input channel, derived channel, totaliser,
counter, timer etc. measured in engineering units (e.g. Degrees Celsius). See also
Measured value.
Relay output
A set of contacts which changes state as a result of a job list being run. Relays are ener-
gised continuously except when ‘in alarm’, so that if power to the recorder fails they go
into their ‘alarm’ state.
Resistance thermometer
Also known as a resistance temperature detector (RTD), a resistance thermometer is con-
structed of a material whose resistance varies in a known way on the temperature it is ex-
posed to. The resistance variation is non-linear, but for any given type, this non-linearity is
well known and invariable and is compensated for by linearisation tables in the recorder
memory.
Retransmission output
See Analogue output.
Setpoint
Also known as ‘threshold’, this is the point at which an alarm becomes active or inactive.
See also hysteresis.
Shunt
The input circuit of each recorder channel measures voltage signals. If current signals are
connected to the recorder, a low value resistor must be placed across the inputs, to convert
the current signal to Volts, according to Ohms law (Volts = Amps x Ohms). Thus, a 0 to
20 mA (0.02 Amps) signal applied across a 250
Ω
resistor produces a voltage range of
0 to (0.02 x 250) Volts = 5 Volts.
Such resistors are called ‘Shunt resistors’ or ‘Shunts’ for short, and are usually of very close
tolerance.