Bench & instruments
VISA addressing
Every instrument needs a resource string. Here is what each kind looks like, where to find yours, and what to do when one will not connect.
A VISA resource string is the address of one instrument on one machine. It is not portable between benches, which is why TestFlow asks you for it rather than guessing, and why generated code is checked for hard-coded addresses before it is accepted.
The four kinds
USB0::<vendor id>::<product id>::<serial>::INSTRUSB0::0x05E6::0x2230::9102345::INSTRThe vendor and product ids are hexadecimal and fixed per model. The serial is on the back of the instrument. This is the easiest kind to get right, and the reason aScan is usually faster than typing.
Scanning the bus
In the desktop app, Scan on the address field enumerates the VISA resources actually present and, where the instrument answers an identification query, shows you what each one is. Pick from the list and the address is filled in exactly. This is the recommended route: a transcription error in a serial number is the single most common cause of a connection that will not open.
When an address will not connect
| Symptom | Usual cause | Fix |
|---|---|---|
| Nothing on the bus at all | The vendor VISA runtime is not installed, or the instrument is off. | Install your vendor’s I/O libraries, power the instrument, replug USB. |
| The instrument is listed but will not open | Another program has it open. | Close the vendor’s own bench software. Most instruments allow one session at a time. |
| Opens, then times out on every query | Wrong protocol for the port, or the instrument is in a local or front-panel lock state. | Check socket versus INSTR for LAN. Take the instrument out of local lockout. |
| Works once, then fails | The USB serial number changed, or DHCP moved the instrument. | Rescan. For LAN, give the instrument a static address or a reserved lease. |
| Connects but returns garbage | Serial settings mismatch. | Match baud, parity, and stop bits to the instrument. |