Tidal Engineering Synergy Series Technical Manual page 211

Derivative – Dn
The derivative portion of the controller output is proportional to the rate of change of the error.
Derivative Output = 100/(proportional band) * Rate * d(error) / dt
Proportional Output – Pn
Proportional output is the difference between setpoint and actual value divided by the proportional
band. As an example: if the proportional band is 10 and the actual temperature is 90C and the
setpoint is 100 then the Pn term is 100%. When the actual value reaches 95 degrees the Pn term is
at 50%, at 99C the Pn term is 10%, at 100C the Pn term is 0%.
Reset Constant
Reset controls the integration error. The larger this value the faster the integration term will change.
Increasing reset adds gain to the system. A lower Reset slows the controller response and
increases stability.
Cycle Time Constant
Cycle Time controls the time period of the proportional cycle. The output goes through one on -off
cycle each cycle. Shorter cycle times reduce the size of steps on the output but increases wear on
output devices such as valves. Longer cycle times increase the size of steps but also increases the
life span of certain chamber hardware.
Optimum test chamber performance criteria depend on the application and can be summarized as follows:
1. Minimum over-shoot.
2. Minimum transition time
3. Minimum energy.
The latter being important when LN2 or electricity consumption is the primary concern.
Synergy Controller Technical Manual, Revision H Page 211