Problem with PID.vi

[hora]

I'm using LABVIEW 4.1 with PID Toolkit
I use PID VI.
I try to use it in an furnace control but
doesn't work.
For example, with a set point of 50% output stay still to a level of
25% with the PV following this value.

What could be the origin of this problem?

Does anyone succeed in working perfectly with PID VI from NI?
Advices are welcome

[DavidT]

Hello hora,

My first bit of advice would be to see if you have tuned your PID correctly. It would seem to me that you have proportional gain (K) but no integral (I) to eliminate your SP-PV error.

[Ben]

Also watch the "reinitial (F)" input.

This input should be true only on the first call and false for all calls thereafter.

Failing to drive this input correctly will eliminate the effects of the "I" and "D" terms.

Ben