I am trying to use gpib/scpi commands to set magnet field strength for the 735vsm. As a first pass I am trying to do this with the COUT command, but the way to specify the field strength makes no sense at all. Its description is as follows:
COUT Manually set field output.
Sent: COUT XXXXXXXX[term]
Returned: Nothing. Return requires COUT?.
Remarks: The X field is an eight character ASCII representation of a binary floating point number in
percent of full scale field output. Use COUT when CMODE = 0. The range and resolution are
-100.000 to +100.000%. Default 00000000 (0%).
NOTE: COUT ends an active ramp and forces field output to the COUT setting value. COUT?
is always active and will not stop a ramp.
I am totally baffled by what this means. Not enough information is provided to figure out how to tell it I want 10% field or 0.5% field strength.
So far I have discerned that the value set must be exactly 8 characters long and each character must be a hex value (0-F).
It's incredibly confusing and honestly makes no sense to have done it whatever way they did it. Like if 00F00000 is 43.73Oe then why is 01000000 not one increment more than it, but is instead 0 again?! But then if that position didn't matter why does making it 01FF0000 suddenly double the value compared to 00FF0000.
Post by Lake Shore Cosmin on Feb 24, 2020 12:54:55 GMT -5
Hello, The Model 735 is a very old VSM controller, part of 7300 VSM hardware. The VSM, as a measurement system, is provided together with a comprehensive software called IDEAS VSM. This software is free and covers all VSM measurements. The support regarding 3rd party programing used for Model 735 was limited, by our knowledge, to providing the IEEE commands. These can be found in the IDEAS VSM help. Please see attached the screen capture.
Yes, previously I have been using the IDEAS VSM software to control the electromagnet system. Currently, I am not trying to do VSM measurements with the system but am instead using it as an electromagnet as part of a separate test. I am hoping to automate the testing so that I don't need to manually change to different field values every 20 seconds. I am attempting to use the IEEE command COUT to change its value. But the description for that command and others like it confusing. I am not yet concerned with being able to specify the exact field value with calibration using the hall probe, but the nonlinear behavior shown when trying to set the field/current value using cout.
Some additional examples of how the hexcode to ramp value seem arbitrary. It is clear that the MSB in the 32bit binary representation corresponds to the positive or negative value. What's not clear is why the hex codes arbitrarily jump at 114 to 115 or any of the other numbers.