The structure for your hotplate project needs a lot of work.
Use subVIs and when you do use subVIs, make sure to give them meaningful icons.
Any for loop with only a single iteration doesn't need to be there.
Add a 100 ms wait to your first while loop. As it stands, it will consume 100% of the CPU while it polls the start button.
Don't do = comparisons for floating point numbers.
What's the model number for the hotplate? I'm guessing there may be an issue with the timing or commandset.
there is a commandset but it isn't available online, command and data sned in a speed of 9600 BPS and N, 8, 1 format, i will try to get these pages available for you,
the main problem seems to be the VISA read unfunctionality. VISA write commands are sent OK but when it has to read from the buffer it gets a time-out error. what could be the reason for this??
Is the interface to the hotplate actually RS-232? I didn't see a VISA Configure Serial Port VI in your hotplate.vi. If you actually are communicating over the serial port then I think you need to configure it first.
You may just need to configure the appropriate termination character.
Clearing buffers can be done by Visa Clear which you have prior to your event structure. Here is also a related Discussion Forum on the timeout topic.
For the termination character it doesn't seem to matter what I put. It resorts back to "A" which is the default case /n . hopefully the delays/waits will help between the write/read? but i've done this earlier so i don't think it seems to help... maybe if i shorten the time?
I just noticed that your while loop where you open the VISA resource executes twice. The second time it tries to open the VISA resource, you're probably getting an error which prevents the subsequent read/write operations from occurring.