Test measurement systems frequently provide for calibration procedures to account for the fact that such systems generally suffer from some degree of signal degradation. For example, measurement instruments do not always have flat frequency responses; cables used to connect different elements in a measurement system are not lossless, switches and filters will typically introduce some frequency dependent losses, and amplifiers can also add some nonlinearities if operated over an extended frequency range. Thus, to obtain accurate measurements it is necessary to measure the performance of the system and to mathematically account for the system performance in the measurement data. This process is sometimes referred to as calibration, or error correction, or alignment.
In many instances fixed configuration measurement systems are used to measure devices. The devices being tested are generally referred to as devices under test (DUTs). These fixed configuration measurement systems are sometimes implemented within an instrument box, and a DUT can be connected to ports of the fixed measurement system. In such systems a signal source in the instrument box will transmit a signal through various components also secured in the instrument box, and then this signal will be applied to the DUT. The measurement signals are then received by a receiver module, also secured in the instrument box, after the signal from the source has been reflected off of, or transmitted through, the DUT.
In some respects calibration of a fixed measurement system is a relatively standard operation, as the basic configuration of the components of the measurement system is fixed. In other situations, variable, or configurable measurement systems, which are often synthetic measurement systems, where different system components can be easily interchanged in the system and different system components are generally separately packaged and can be connected via cables and potentially other connecting devices, are used. Various specific test configuration set ups of such systems are sometimes referred to as test program sets (TPSs). In such configurable test systems, various system components are coupled together as a measurement test system and the operation of the various components of the systems are controlled by a controller, or an external processor which is coupled to components of the system. In some cases, software tools are provided which can be used to aid in programming the processor to control the operation of the various components in a given system to provide for desired measurements. In the past, the programming of the processor also provided for specific calibration procedures which were unique for each of the various combinations of components of the system, and the calibration process was generally included as part of test sequence which was used for a specific configuration.
For instance, a test program might instruct the operator of configurable system disconnect a cable from a DUT and to connect the cable to a different test port of the configurable system so that the performance characteristics of the system without the DUT can be measured, and then when the DUT is connected to the system, the loss of the cables, and other specific system operational characteristics could be mathematically removed from the final measurement data.
This calibration process for configurable systems has in the past been largely application specific, and requires particular steps in the test program. A different test program will usually require different calibration sequences, even if the same hardware components are being used. Further, the calibration sequences assume specific hardware configurations. If the test system is changed, or even if one component of the system is swapped out for another similar component, the calibration procedures will generally need to be reexecuted. Many past calibration procedures include multiple steps, where each step provides a particular type of performance information, which is not utilized by other steps in the calibration process.