Let’s learn more about the logging and fast logging functionality of R&S®NGM and R&S®NGL. The associated application program provides charting functionality for logged voltage, current and power values.
Standard logging records timestamps together with readings for voltage, current and power for each available channel. It is always global for all available channels of the power supply. The measurement interval can be set in the range between 0.1 second and 600 seconds. The start of the logging can be triggered either by an internal event or by an external trigger signal.
The sample rate and duration of standard logging can be specified in four modes:
- Unlimited mode: When started, the logging runs until it is stopped. In this mode the interval (sample period) can be specified.
- Count mode: When started, the logging collects the specified number of values and then stops. In this mode the interval (sample period) and the number of sampled values can be specified.
- Duration mode: When started, the logging runs for the specified duration. In this mode the interval (sample period) and the duration of the logging can be specified.
- Span: Logging starts at the specified date and time and runs for the specified duration. In this mode the start time, the interval (sample period) and the duration of the logging can be specified.
While R&S®NGL power supplies offer the standard logging functionality, they do not provide the fast logging as R&S®NGM does. The R&S®NGM power supply series is a high-precision source and sink with high-speed voltage and current logging capability.
How does fast logging work on R&S®NGM power supply?
It records voltage and current readings versus time, but without time stamps. Fast logging is always individual to each channel of the power supply. It can be configured, started and stopped in each channel independently. The data is collected in separate files. Like the standard logging, the fast logging can also be started by a trigger event configured locally in the menu. For fast logging, it is recommended to select a fix current measurement range if the maximum expected current is known. This ensures that logging data is continuously available.
For fast logging, a sample rate has to be selected out of an available set. The fast logging runs for the specified duration after it has started. Available sample rates for fast logging are 15, 30, 61, 122, 244, 488, 976, 1953, 3906, 7812, 15625, 31250, 62500, 125000, 250000 and 500000 values per second.
Remote control connection
R&S®NGM or R&S®NGL can be operated remotely, either via USB, LAN or GPIB connection between the controlling PC and the power supply. In remote control mode, the logging data must be collected via the remote control interface every time the system reports new data to be available. The interface used for the remote connection must support the resulting data rate.
There are some measurement requirements to be mindful of when using remote control functionality, since the fast logging function of the DC power supply R&S®NGM requires a certain minimum data rate, depending on the sample rate of the logging function. The data rate of GPIB is sufficient only for the lower sample rates of the fast logging function. Therefore, GPIB is not recommended as connection to the R&S®NGM for this application.
The USB interface in the R&S®NGM and R&S®NGL supports two different USB classes. The “CDC” class emulates a serial interface via USB-to-serial converter and has the advantage of compatibility with older remote control systems. Since the data rate of the “CDC” class is not sufficient for fast logging, the “TMC” class needs to be used.
Save logging data locally to files, and display them in charts
Standard logging data is originally stored locally, either on internal memory or to a USB stick connected to the R&S®NGL or R&S®NGM. The location of the log file must be selected locally in the menu. As standard logging data is primarily stored on the power supply, display and storing of standard logging data is only possible with a power supply connected. Standard logging files contain voltage, current and power readings for one or two channels. User can choose specific power supply channel as a data source and display the data in a form of a diagram. While the respective voltage and current data can be displayed in one diagram, power data is always displayed in a separate diagram. Before the diagrams can be created, the data has to be transferred from the power supply to the controlling PC over the remote control interface.
Fast logging data is stored in floating-point raw format. If started manually, it is stored to a USB memory stick connected to the R&S®NGM, which must support the resulting data rate. During fast logging, data is transferred from the R&S®NGM to the controlling PC in real time and saved every 0.5 seconds. Each logging operation generates about two data files per second. The file size depends largely on the sample rate of the fast logging. The file name consists of date and time, sample rate, channel number and a sequential number. The log data of the selected file or of the complete fast log to which the selected file belongs, is displayed, depending on the settings. After termination of the logging, the data can be exported resp. converted offline to a character separated ASCII format.
You can find more information about logging tool on R&S®NGM an R&S®NGL power supplies in this AppNote!