What is the difference between an "ECal Confidence Check" and a Network Analyzer "System Verification" test?
ECal Confidence Check:
The ECal Confidence Check is a method to check the accuracy of a calibration performed with either a mechanical cal kit or an ECal module. It is not a method for verifying the performance of the analyzer.
The ECal Confidence Check allows the user to measure a known impedance state within the ECal module. This known impedance state is referred to as the ‘confidence state’. The confidence state is compared with factory measured data stored within the ECal module. The analyzer simultaneously displays the confidence state data (as a dynamic data trace) and the factory measured data from within the ECal (as a memory trace).
In order for the ECal Confidence test to be valid the test ports of the ECal module must be connected directly to the calibration reference plane without adapters. If the two traces (the dynamic trace and static memory trace) exhibit excessive variation this may be an indication of:
- Loose, dirty or damaged connection at the test ports
- Poor or damaged test port cables
- ECal module out of tolerance
- ECal module with damaged connectors
If an ECal confidence check reveals discrepant data then carefully inspect the cables and connections and if necessary clean and gage each connector including those of the ECal Module. Repeat both the calibration and ECal confidence test. If the ECal Confidence Check tests results are still suspect, this is an indication of possible instrument failure, ECal failure, connector damage, etc. Attempt to isolate the cause of failure and return damaged items to Agilent Technologies, Inc. for evaluation and repair.
Additionally, Agilent Technologies does not provide specification limits or parametrically define "excessive variation” as applied to the ECal Confidence Check. Assuming all cables and connectors have been verified the interpretation of ‘excessive variation’ as applied to the ECal Confidence test results is left to the user for interpretation.
Agilent recommends that upon receipt of a new ECal module, the user performs the confidence check and saves the measurement results as a baseline for future reference. Periodically, it is recommended that additional ECal confidence checks be executed and the test results be compared to the baseline data.
ECal confidence checks should be performed at narrower IF bandwidth settings, 1KHz or lower, in order to minimize trace noise effects, and improve repeatability of test results.
System verification testing provides network analyzer users a method to verify that the network analyzer measurement system is operating and providing acceptable error corrected measurements. A network analyzer measurement "system" includes the analyzer, calibration kit, test cables, and any necessary adapters. System Verification requires the use of an analyzer user calibration (via either a mechanical calibration kit or ECal) and a system verification kit. System verification relies on measuring known devices (other than calibration standards). The verification kit components (standards) magnitude and phase response are well characterized and the inherent uncertainties are defined based upon the analyzer under test. Verification kits include precision airlines, mismatch airlines, and precision fixed attenuators. Traceable measurement data is shipped with each verification kit. Verification kits can re-certified by Agilent.
The system verification utility confirms the network analyzer system is operating properly by automatically measuring the magnitude and phase for all four S-parameters for each verification device and comparing the values against the following:
- Factory measured data as acquired from files on the verification disk / USB pen drive
- Limit lines based on the measurement uncertainty
The PNA, PNA-L, PNA-C and PNA-X, E5071C ENA, and Agilent ‘Legacy’ analyzers (8753, 8719, 8720 and 8722) series network analyzers support system verification via embedded utilities within the analyzer's firmware.
The E5070A/71A/70B/71B/72A ENA, E5061A/62A, E5061B and Agilent ‘Legacy’ 871x Series analyzers do not support System Verification. For these analyzers, one alternative to performing system verification is to measure the responses of mechanical open, short and load standards after performing a calibration using an ECal module. This can provide the user with a ‘system confidence’ check at a much lower confidence than formal system verification.