How does the multimeter collect and detect electrical intermittent faults?
Unstable intermittent electrical faults are the most difficult things in fault diagnosis: it is difficult for people to capture some electrical parameters when the fault occurs. If fault parameters are captured when a fault occurs, the fault diagnosis process will be simplified to a considerable extent. However, intermittent failures usually occur after the system power is turned off. At this time, it is difficult to find the source of the problem. When a fault occurs, being able to determine the fault status and perform electrical measurements are the two biggest challenges in tracking intermittent faults.
There are many test equipment that can make intermittent fault diagnosis simple. These devices include complex signal analyzers and digital oscilloscopes, as well as easy-to-use handheld multimeters. This article mainly introduces how the multimeter collects and detects electrical intermittent faults?
1. The functions required by the multimeter that can capture intermittent faults The digital multimeter also needs a measurement recording function on the basic measurement function (AC voltage, DC voltage and resistance measurement). Through the combination of standard tables, the multimeter can detect intermittent Fault parameters of the fault.
Previously, people used mechanical paper tape recorders to continuously record voltage or current. In work, they need to connect voltage to the input, or clamp the current sensor on the wire, and the recorder will print the changes in voltage or current on the paper tape. In this case, the maximum length of the recording depends on the amount of paper on the paper tube.
Now, digital multimeters with digital acquisition or storage functions have the same band-shaped recording function through the computer or their own memory.
If the digital multimeter has the function of the minimum/maximum/average recording mode, like the paper tape recorder, the digital multimeter also reads the input reading at a certain interval. But unlike each tape recorder that saves each reading, the reading is compared with the previously saved reading to determine whether the value is higher than the previous maximum value or lower than the previous minimum value; if it is, the new reading Replace the value originally stored in the high or low reading register. After a period of recording, you can call up the values of these registers for display and view the maximum and minimum values during the recording time.
2. How does the multimeter record intermittent faults? Use the multimeter's minimum/maximum/average recording mode and select the corresponding functions (AC voltage, DC voltage, resistance, AC current, DC current and frequency) according to the measurement items to ensure that the test is connected before the minimum/maximum/average function Circuit, otherwise the minimum reading will always be the environmental value before the test line is not connected. This will affect the analysis of the recorded data after the end of the recording time; activate the min/max/average recording mode, the multimeter will indicate the maximum reading on the display, and will beep when a new maximum or minimum value is detected sound.
The advantage of this is that while ensuring that the digital multimeter will not be disturbed and will not pose a security risk to anyone, you can leave the digital multimeter in place for measurement and focus on other tasks. At any time during the recording cycle, you can view the saved readings, or pause the recording mode without deleting the saved readings.
3. How does the multimeter mark the recording time? The time when the minimum and maximum values are detected is very useful information for determining the cause of intermittent failure. The DMM can store the amount of time from the start of recording to the storage of a new minimum, maximum, or average value in the minimum/maximum/average recording mode. Therefore, each stored minimum, maximum and average has a "time stamp" corresponding to it.
As long as the time to activate the min/max/average recording mode is recorded separately, you can easily calculate the actual time when the digital multimeter detects the reading. For example, suppose you activated the recording mode at 3:07:00 PM, and the time stamp of the displayed maximum reading is 47:05. Simply add the time stamp and the start time to determine the time when the maximum value is recorded. .
Utilizing the minimum/maximum/average recording mode of the digital multimeter, it is very effective for the diagnosis of intermittent faults. However, it assumes that the connected circuit point can show the maximum or minimum value when the fault occurs; if the reading caused by the intermittent fault is between the maximum and minimum values, then the min/max/average function Too helpful to determine the cause of intermittent failure.
During the measurement in the minimum/maximum/average recording mode, do not disconnect the test line from the circuit under test before pressing the HOLD button to stop recording, or viewing and archiving all saved values. Disconnecting the test line during recording will cause the multimeter to process the value that appears on the disconnected test line and affect the average value saved when the test line is connected, and may affect the stored minimum or maximum value.
4. How does the multimeter continuously record intermittent failures? Some multimeters not only have the minimum/maximum/average value recording function, but also combine this function with another function called AutoHOLD and a larger memory to form an event logging (Event Logging) function.
The automatic hold function can sense when the measurement signal becomes unstable and when it becomes stable again. Using the automatic hold function to trigger the start and stop of the minimum/maximum recording function makes the digital multimeter not limited to detecting faults that produce minimum or maximum values.
If the multimeter has an infrared RS232 interface, the continuous recording function will be more powerful, and it can become a simple event collector to transfer the data collected by its multimeter to the computer. Using a computer, you can conduct a detailed analysis of each stable and unstable event. You can view not only the minimum and maximum values in each stable and unstable cycle, but also the start and end time of each cycle. In addition, the average value of each cycle is also recorded. At the same time, it can dynamically detect the change trend graph of voltage or current.