eBIRST Switching System Test Tools provide a convenient way of measuring the resistance of paths in switching systems at the switching system connector.
eBIRST is capable of making accurate measurements of resistance and the tools include within them a set of a precision resistors that it uses to derive calibration data before conducting the measurement. The tools measure these resistors and uses the data to set the resistance scales. For most users there is no need to do anything more.
However, some industries have more demanding process requirements, especially where safety issues are involved, and procedures may demand that any maintenance tools can be independently verified - and the calibration resistors in the eBIRST tool are not externally accessible. In addition the user may wish to ensure that the MUX that is used to connect the measurement engine to the switching system connector is also working correctly. These users may wish to consider purchasing calibration fixtures.
How eBIRST works
The measurement engine first connects to the calibration resistors to derive calibration data for the test settings used for the measurement.
Once a test is underway it uses the 4 wire multiplexer to access the eBIRST tool connector to an adapter or directly to the switching system connector. For more information on eBIRST operation, take a look at our article How eBIRST Works.
Two scenarios can be envisaged where problems might arise, if the internal calibration resistors changed value it would give misleading results since they are used a reference, if the MUX fails it will indicate faults which are not present in the switching system. Neither situation is very likely because the calibration resistors are infrequently used and subject to only low signal levels, the MUX uses solid state switches and also only gets used at low signal levels.
Application Accuracy Requirements
Measuring switch path resistance does not require high accuracy to diagnose problems though eBIRST is capable of doing this with high resolution. The path resistance of switching systems is often dominated by copper tracks or wires and these will have a temperature coefficient of the order of 0.39% per C change in temperature. So differences of a few % can be generated just by changes in environmental conditions even in office environments.
Even so, approval systems may still demand independent verification. For that reason we can supply Calibration Fixtures to users who have a requirement for independent verification.
Functional diagram and image of eBIRST Calibration Fixture
For each eBIRST tool type a calibration fixture is available which provides two functions:
- Provides a back to back connection between two tools that allows the application program to conduct a test through the multiplexers of the two tools
- Provides a set of calibration resistors, similar to those used in the eBIRST tools, which can be connected to an eBIRST tool. These resistors can be also checked with a user provided DMM that is traceable to standards for resistance measurement using a 4-wire connection.
The eBIRST application program provides a facility for conducting the back to back test for the MUX's. The calibration resistors in the eBIRST tool can be compared to those in the Calibration Fixture using the same measurement method as the tools uses for measuring the calibration resistors in the eBIRST tools.
The tests confirm the tools are working correctly through their multiplexers and that the measurement is confirmed to be providing the required accuracy.
Using a user provided DMM verification that has traceability through the DMM calibration process the calibration resistors in the Calibration Fixtures can be checked. The DMM can be any model with 4 wire resistance measurement capability and is therefore likely to be in common use by users.
Consequently for those users who want a verification system we recommend the use of two eBIRST tools and the Calibration Fixture. Users who are less concerned about verification of the tools (bearing in mind a MUX failure will produce apparent switching system faults) can elect not to purchase the Calibration Fixture or the second eBIRST tool. Some users may wish to have a second tool for master slave testing, but the tools must be the same type. For users who only need to establish a traceability route they have the option of buying the Calibration Fixture but not a second eBIRST tool on the basis that MUX faults will incorrectly indicate switching system faults.