Instrumentation Monthly Test | Measurement | Control
In addition to electrical signals, memory recorders provide input modules for myriad measurement parameters, including temperature, pressure, vibration, frequency, weight, acceleration and rotation.
Oscilloscopes are useful for observing real-time signal traces but when measuring mechatronics-controlled circuits for example, there is always the possibility of short-circuits or ground faults because the ground connection is common between the two channels of a typical oscilloscope.
Where there is a mix of strong and weak signals or there are differences in the electrical ground of the measurement circuit, memory recorders offer individual channel isolation, providing a secure method for analysing waveforms.
A memory recorder can be likened to an oscilloscope with large number of analogue and digital inputs, and all the waveforms can be seen on the screen at the same time in various user selected colors.
Input Modules
The HIOKI MR8827 is an advanced waveform monitoring tool offering 32 analogue channels, the number of which is expandable using optional modules. Plug-and-play input modules allow customers to measure a variety of parameters to a single memory recorder.
Hioki’s advanced memory recorders pair with a variety of modules, such as basic Analogue Modules that allow direct electrical input up to 400V DC or 200V AC, and High Voltage and High Resolution Modules that provide direct input to 1000V DC for applications such as fuel cell stacks, affording a high sensitivity range to measure voltage with high precision.
Temperature Modules support a variety of thermocouple sensor inputs, both voltage and temperature, from two to 16 channels to be scanned.
Strain Modules get their input from gauge distortion readings to measure physical acceleration attributes such as weight, pressure, displacement and torque, while Charge Modules feature a built-in anti-aliasing filter to support input for piezoelectric acceleration pickup sensors – both charge output and pre-amp types.
FFT Analogue Modules with built-in anti-aliasing filters are primarily used for Fast Fourier Transform analysis of recorded signals to display their individual frequency components.
Frequency Modules measure the frequency fluctuation of power voltages, perform integration and measure duty ratio, while Current Modules are used in combination with clamp-on sensors and RMS Modules are used to record specific Root Mean Square fluctuations.
For motor manufacturing industry, CAN Modules capture data from a CAN bus, measuring vehicle parameters such as engine rotation, water temperature, vehicle speed and tyre pressure.
Triggers
High-end memory recorders offer up to eight different triggers. While the basic triggers are available in all memory recorders, from Simple Level Triggers that activate recording as soon as the preset detection level has been exceeded, to Voltage Drop Triggers that are convenient for monitoring commercial power voltages.
By setting the appropriate AND/OR logic conditions between the trigger and source, measurement and recording occurs either when all trigger conditions are satisfied; the AND state, or when only one is satisfied; the OR state. The typical triggers are:
1) Level Trigger. When the signal rises above or falls below the set voltage value, a trigger occurs. This is the simplest type of trigger, similar to an edge trigger found in many oscilloscopes.
2) In Window and Out Window Triggers. Recording or measurement can be set to start when the signal falls within the preset upper and lower thresholds. An example of how this type of trigger would be effective is when slowly fluctuating temperature levels need to be monitored at certain ranges.
3) Period In and Out Triggers. The period of a rising or falling voltage signal is first measured, and if the period falls within or outside the reference cycle, a trigger occurs. This is useful for detecting abnormal frequencies.
4) Glitch Trigger. Triggering occurs when the input signal crosses the threshold voltage, either when rising or falling, and when its pulse width is shorter than the reference width. This is effective for detecting abnormal pulse width.
5) Voltage Drop Trigger. Specifically for 50/60Hz commercial power supplies, triggering occurs when peak voltage drops below the specified level for more than one-half cycle. This can be used for detecting instantaneous power outages.
6) Waveform Judgment Trigger. Triggering occurs when the reference waveform range is exceeded. This is effective for commercial power supplies or for repeatability analyses using waveforms to detect abnormalities.
7) Event Trigger. When the number of activated triggers reaches a preset number, recording begins.
8) Logic Trigger. A trigger is applied when a pre-determined signal level pattern out made up of a combination of 1, 0, and X occurs.
Summary
Measuring signal parameters like electrical power, voltage and current, temperature, pressure, vibration, frequency, weight, acceleration and rotation, can be enhanced by the appropriate utilisation of tiggers and logic states to yield real-time monitoring of plant variables.