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.

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.

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 nputs 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

Level trigger on analogue inputs when trigger exceeds user selected level

Window trigger on analogue inputs when trigger signal goes into or out
of a user selected window range

Voltage drop trigger used on AC power lines when the peak value falls
below the setting value

RMS level trigger where the RMS value crosses the set value

Period trigger used when a rising or falling edge does not fall within the 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 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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