User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDEB2.6.2 OUTPUT LIMITS (Cont.)Notes (Continued)3. The tightest limits (between Remote and PID) are connected to the output where an overall limitis applied using parameters ‘Output High’ and ‘Output Low’.4. ‘Working Out High’ and ‘Working Out low’ found in the Diagnostics list are read only parametersshowing the overall working output limits.5. The tune limits are a separate part of the algorithm and are applied to the output during the tuningprocess. The overall limits ‘Output Hi’ and ‘Output Lo’ always have priority.B2.6.3 Output Rate LimitThe output rate limiter is a rate-of-change limiter, set in (%/sec) which prevents step changes in output powerbeing demanded. Rate limiting is performed by determining the direction in which the output is changing,and then incrementing or decrementing the Working Output (Main menu) until it equals the required output(Target OP).The amount to increment or decrement is calculated using the sampling rate of the algorithm (125ms) andthe selected rate limit. If the change in output is less than the rate limit increment the change takes effectimmediately.The rate limit direction and increment is calculated on every execution of the rate limit. Therefore, if the ratelimit is changed during execution, the new rate of change takes immediate effect. If the output is changedwhilst rate limiting is taking place, the new value takes immediate effect on the direction of the rate limit andin determining whether the rate limit has completed.The rate limiter is self-correcting such that if the increment is small it is accumulated until it takes effect.The output rate limit is active when the loop is in both auto and manual modes, and during autotune.B2.6.4 Sensor Break ModeIf a Sensor break is detected by the measurement system the loop reacts in one of two ways, according tothe configuration of ‘Sbrk Mode’ (‘Safe’ or ‘Hold’). On exit from sensor break the transfer is bumpless – thepower output starts controlling again from the current operating setpoint and moves, under PID closed-loopcontrol, from its pre-set value to the control value.SAFEIf set to ‘Safe’, the output adopts a pre-set level (Sbrk OP). If rate limit is not configured, the output steps tothe Sbrk OP value, otherwise it ramps to this value at the rate limit.HOLDIf set to ‘Hold’ the output remains at its current value. If Output Rate Limit (Rate) has been configured a smallstep may be seen as the working output will limit to the value existing two iterations ago.B2.6.5 Forced OutputThis feature enables the user to specify what the output of the loop should do when moving from automaticcontrol to manual control. The default is that the output power is maintained but it is then adjustable by theuser.If Manual Mode is set to ‘Step’, the user can set a manual output power value and on transition to manual theoutput will be forced to that value.If Manual Mode is set to ‘Track’ the output steps to the forced manual output and then subsequent edits tothe output power are tracked back into the manual output value.If Manual Mode is set to ‘Last Man. Out’ then when moving from automatic to manual mode, the outputadopts the last manual output value.HA030554Issue 7 Nov 12Appendix BPage 321