Uncertain intermittent electrical faults are the most difficult things for all people who diagnose faults, mainly because they are difficult to schedule. If the fault phenomenon can be observed when a problem occurs, the fault diagnosis process will be simplified to a considerable extent. However, as the saying goes, "I can't eat hot tofu," the same applies to intermittent electrical problems. When there is a fault, being able to demonstrate and be able to make electrical measurements are the two biggest challenges in tracking intermittent faults.
There are many test tools that make it easier to diagnose intermittent faults. These tools include sophisticated signal analyzers and storage oscilloscopes, as well as handheld digital multimeters (DMMs). Of course, you may not have these tools available, or the location of the fault makes it difficult to use a bulky analyzer to the point of failure. Using a digital multimeter, you can get a lot of information about intermittent failures without having to return to the office to carry bulky storage oscilloscopes to the job site. This article describes how to use the DMM as a diagnostic tool for intermittent failures.
Digital Multimeter functionality that can be used to capture intermittent faults
Combining the DMM's basic measurement functions (AC voltage, DC voltage and resistance measurement functions) with the measurement record table function, the user can detect intermittent faults. Before long before you can buy voltage or current measurement tools using a mechanical tape recorder. Just insert the voltage on the input, or clamp the current transformer on the wire, and the recorder will record progressive marks on the tape under the pen. The maximum length of the recording depends on the amount of paper on the paper roll. In some digital multimeters, the same strip recorder function is also integrated.
Fluke's 170 and 180 Series DMMs have a function called Min/Max/Average Record Mode. Like a tape recorder, the DMM reads the input reading at regular intervals. However, unlike saving each reading, it compares the reading with two previously saved readings to determine if the value is higher than the previous maximum or lower than the previous minimum. If so, the new reading will replace the original value stored in the high or low reading register. After a period of recording, you can recall the values ​​of these registers and display them to see the maximum and minimum values ​​during the recording time. As an additional feature, these DMMs can also calculate and store the average of all readings over a given period of time.
Follow these steps to use the Min/Max/Average Record mode:
1. Select the appropriate function (AC voltage, DC voltage, resistance, AC current, DC current, and frequency) according to the measurement item.
2. Connect the DMM's test leads to the circuit under test. Fluke's SureGrip test leads and probes provide a variety of circuit connections. Make sure to connect the test circuit before activating the min/max/average function, otherwise the min reading will always be the ambient value before the test line was connected. This will affect the analysis of the recorded data after the recording time is over.
3. Press the RANGE button to switch to manual range. If necessary, press the RANGE range repeatedly until the Meter displays the correct range. This step is necessary because it will automatically switch to manual range mode when the DMM is set to Min/Max/Average Record mode. You cannot change the span setting once the min/max/average function is activated.
4. Press the MIN MAX button to activate the Min/Max/Average Record mode. In the Fluke 170 Series, the maximum reading is indicated on the display and a beep sounds when a new maximum or minimum is detected; in the Fluke 180 Series, the main display shows the maximum reading and the secondary display The screen will show the current measurement.
To ensure that the DMM is not tampered with and not pose a security risk to anyone, you can leave the DMM in place to measure and concentrate on other tasks. At any time during the recording cycle, you can use the method described in the next step to view the saved reading or press the HOLD button to pause the recording mode without deleting the saved reading. Press the HOLD button again to continue recording.
1. Press the button MIN MAX to see the saved reading. Each time the button is pressed, the saved values ​​(min, max, and average) are displayed sequentially on the display of the Meter.
Record time stamp
The time when the minimum and maximum values ​​are detected is very useful for determining the cause of the intermittent failure. The Fluke 180 Series Digital Multimeter can store the amount of time between the start of recording and the saving of a new minimum, maximum, or average value in the Min/Max/Average Record mode. Therefore, each saved minimum value, maximum value, and average value have a corresponding "time stamp".
You can easily calculate the actual time when the DMM has detected the reading as long as you record the time during which you activated Min/Max/Average Record mode. For example, suppose you activated the recording mode at 3:07:00 PM, and the maximum reading time stamp shown is 47:05. Simply adding the time stamp and start time will determine when the maximum value will be recorded. . In this example, the maximum time recorded should be 3:54:05 pm on the same day.
With the Min/Max/Average recording modes of the 170 and 180 Series DMMs, the diagnosis of intermittent faults is very effective. However, it assumes that the connected circuit point can exhibit a maximum or minimum value in the event of a fault; if the intermittent fault causes a reading between the maximum and minimum values, then the minimum/maximum/average function will not Too helpful in determining the cause of an intermittent failure.
prompt:
Do not disconnect the test leads from the circuit under test until you press the HOLD button to stop recording or view and archive all saved values. Disconnecting the test line while recording will cause the Meter to process the value appearing on the broken test line and affect the average value saved when the test line is connected, and may affect the saved minimum or maximum value. .
Advanced min/max recording function
The Fluke 189 true RMS multimeter not only has the standard minimum/maximum/average value recording function as described above, but also combines this function with another function called AutoHOLD and a larger memory. Formed Event Logging function.
The automatic hold function can sense when the measurement signal becomes unstable and when it is stable again. Using the automatic hold function to trigger the start and stop of the min/max recording function makes the DMM not only limited to detecting those that produce the minimum or maximum value.
To use the event logging feature, you need the Fluke 189 True RMS Multimeter, the FlukeView® Chart Archiving Software, and the computer used to download and view recorded data. The digital multimeter can be brought to the site where the recording is required and recorded during the time period when an intermittent failure may occur. You only need to use the software and PC after you have finished recording.
Follow the procedure described in Min/Max/Average Recording Mode above to select the appropriate measurement function, manually set the range, and set the digital multimeter. Connect the meter's input to the measurement point and activate the event logging function.
Like the min/max/average record modes, the DMM starts to store the maximum and minimum values ​​in memory. As long as the measured signal is within a certain percentage of the selected range, the DMM will update the saved minimum and maximum values ​​of the same group as the minimum/maximum/average record mode; however, if the input signal is If the change exceeds a certain percentage of the range, the DMM will save the collected minimum and maximum values, as well as their relative time stamps, and begin to collect another set of minimum/maximum values ​​until the measurement signal is stable. Once the signal has stabilized, the meter will hold the minimum and maximum readings for that period and start collecting a new set of minimum/maximum values ​​during the stabilization period. As long as the recording task continues, the multimeter will continue to repeat the above process or stop when the memory overflows. Based on the multimeter's settings, the multimeter's memory can hold up to 3 days of min/max data pairs.
figure 1
In the PC, the recorded data can be displayed in the table format shown in Table 1 or in the graphic format shown in FIG. Observe line 3 of Table 1 and you will see the third cycle begins at 9:53:30 am on July 4, 2000. The duration of the event is 1 minute 20.6 seconds. During this period, the maximum value was 8.1 amps and the average of all readings was 7.7 amps with a minimum of 7.5 amps. The surrounding event was a stable event and ended at 9:54:51 am. As we saw in this example, the event logging function can capture large amounts of data during intermittent cycles.
Yes, locating intermittent faults is really difficult; however, a DMM with proper functionality can help us to track these elusive faults. Fluke's various digital multimeters not only have the function of finding intermittent faults, but also have the ability to catch other faults. Contact your local Fluke distributor or visit Fluke's website to find the test tool that best suits your needs.
E
Start Time
Duration
High
Average
Low
Description
Stop Time
1
9:21:15 AM
32:14.7
0.0 A ac
0.0 A ac
0.0 A ac
Stable
9:53:30 AM
2
9:53:30 AM
00:00.4
21.2 A ac
12.1 A ac
0.5 A ac
Unstable
9:53:30 AM
3
9:53:30 AM
01:20.6
8.1 A ac
7.7 A ac
7.5 A ac
Stable
9:54:51 AM
4
9:54:51 AM
02:06.5
7.5 A ac
7.4 A ac
7.3 A ac
Stable
9:56:57 AM
5
9:56:57 AM
00:01.1
7.0 A ac
1.0 A ac
0.2 A ac
Unstable
9:56:58 AM
6
9:56:58 AM
58:34.6
0.1 A ac
0.0 A ac
0.0 A ac
Stable
11:55:33 AM
7
11:55:33 AM
00:00.3
20.8 A ac
11.7 A ac
0.3 A ac
Unstable
11:55:33 AM
8
11:55:33 AM
01:23.3
8.4 A ac
8.0 A ac
7.8 A ac
Stable
11:56:56 AM
9
11:56:56 AM
01:59.3
7.8 A ac
7.7 A ac
7.4 A ac
Stable
11:58:56 AM
10
11:58:56 AM
00:00.7
6.6 A ac
1.3 A ac
0.2 A ac
Unstable
11:58:56 AM
11
11:58:56 AM
00:04.5
0.2 A ac
0.1 A ac
0.0 A ac
Stable
11:59:01 AM