Memory Recorders
Memory recorders have been around for years but not much is known about
the application of these instruments and how they can rapidly reduce
development, testing and fault finding time.
A memory recorder is PC friendly and can be likened to an oscilloscope.
Analogue inputs together with a number of digital inputs and all the wave
forms, if desired, can be seen on the screen at the same time in various
user selected colours. The analogue inputs can be related to temperature,
pressure, acceleration, frequency etc. as well as voltage and current.
Even intermittent faults and events happening before they occur can be
recorded for later analysis without a person being present during the event,
and results can also be analysed on a PC.Memory
Each instrument has a built-in non volatile memory to store recorded data
and in many cases the instrument has a built in printer, floppy disc drive or
RS232 interface to communicate with PC's and modems. In addition, a
PCMCIA port is normally included to enable external memory to be added
or a network interface to be installed.
Various modes are possible such as memory mode where all data is stored
in memory for replay, disc storage, printing or analysis, recorder mode for
recording directly to screen, paper or disc, RMS mode to record 50/60Hz
power lines as an RiMS calculated value, and X-Y Mode to allow two input
signal plots to be combined.
Triggering
In order to start recording. the instrument has to have a trigger source; this
is an area providing a great deal of power for the user. In addition to normal
trigger inputs such as external or manual inputs, any analogue or digital
input can be used to start recording, or recordings can be triggered according
to an internal clock timer specifying trigger start/stop times and time interval
between them.
Trigger functions often include:
Pre-trigger settings up to 100% of the recording to capture events which
happened before the trigger occurred
of a user selected window range
below the setting value
cycle range
Another important feature is the cursor facility where two individual cursors
can be superimposed on the screen in either horizontal or vertical positions.
Each cursor can mark positions on the screen and the precise readings in
figures are displayed. When two cursors are used, not only are the individual
readings displayed but also the displacement between them. Many other
functions can be performed with these cursors including the ability to print
out only a section of a recording.Applications
Applications of these instruments are wide and varied and it is not necessary
for personnel to be present while they perform their functions. Some models
have the facility to fax waveforms triggered in a remote location.
Typical applications include PLC or electronic controller input/output timings
and waveforms, circuit breaker timings, engine or motor performance
characteristics, analysis of sequ~nce control devices, recording & analysis
of motor inrush current. detection & analysis of power supply transients and
intermittent fault detection. ASM says that with the combination of user and
PC friendliness, memory recorders are invaluable for today's industrial
environment. There are many examples where days of normal faultfinding
methods have failed but with the help of a memory recorder, diagnosis has
taken less than 30 minutes.
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