How to Obtain a Floating Point Result from SCPI Queries in Python

Learn how to retrieve precise power measurements from a Rohde & Schwarz Spectrum Analyzer using SCPI commands in Python with PyVISA.
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How to Obtain a Floating Point Result from SCPI Queries in Python

When working with instruments like the Rohde & Schwarz Spectrum Analyzer, you might encounter situations where you need to retrieve precise measurements from your queries. A common issue is obtaining floating-point results from SCPI (Standard Commands for Programmable Instruments) commands, particularly when programming with Python and using libraries like PyVISA.

The Problem

Many users, including those working with spectrum analyzers, often find that despite sending commands to retrieve measurements, the values returned are always in integer format. For instance, if you're expecting a power measurement like 21.34 dBm, you might only see 21 dBm in your output. This can be frustrating, especially when the decimal values are crucial for your analysis.

In a recent inquiry, a user reported trying various commands to obtain floating-point results but was only receiving integer outputs. This led to confusion about whether the issue lay in their coding, instrument configuration, or perhaps an oversight in the command structure.

Solution Overview

The primary goal is to properly retrieve the floating-point results using the right methods provided by the PyVISA library. Let’s break down the solution into clear sections:

The Right Command to Use

In PyVISA, there are two essential methods for interacting with your instrument:

write(command): This sends a command to your instrument but does not return results.

query(command): This sends a command and returns the result from the instrument.

To get the measurement you are looking for, you should replace the write method with the query method in your code. Here’s how to do it:

[[See Video to Reveal this Text or Code Snippet]]

Conversion to Float

Once you successfully query the value from your instrument, you may need to convert the returned string value into a floating-point type. In Python, you can easily convert a string to a float using the float() function.

Configuring the Instrument

If you still don’t see decimal points in your results after making the above changes, it's important to check the configuration of your spectrum analyzer:

Ensure that the measurement resolution is properly set on the instrument.

You may need to refer to the user manual for the correct SCPI commands related to SENS:MARK:FUNC:FPE:STAT ON or similar settings which configure measurement precision.

Example Code

Here’s a complete example that integrates all the adjustments mentioned:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In summary, to obtain floating-point results from a SCPI query, use the query method instead of write, and ensure that your instrument is configured correctly for precision measurements. With these steps, you should be able to get the accurate readings you need for your work without complications. Happy coding!