Item - Step

Please refer to Adding a New Item for specific information on how to add an ITEM and how to change its properties.

Description

The Step ITEM is to be used with the Step Master ITEM.

Generally for each step of the Step Control that you set up in a TASK add one Step ITEM.

It does not really matter where in the TASK you place the Steps, however for neatness it is probably best to place them in order before the Step Master ITEM.

As each step is set up there will be a number of ITEMS that it requires to get information from. Remember to ensure that all of these supporting ITEMS are placed just before the respective Step ITEM. This will keep the ITEMS grouped in a logical way. It will also mean that as the TASK is updated the supporting ITEMS will be updated first so that when it is the Step's turn to be updated it will have access to the very latest information from the supporting ITEMS. For more information on the sequence in which ITEMS are updated refer to Overview Operation.

Generally a Step ITEM can be divided into 3 distinct parts:

  1. Step Information - Include the Set Value at the end of the step and the Duration of the step.
  2. Deviation Alarm - If enabled includes the Hi and Lo deviation values required for the deviation alarm.
  3. Guaranteed PV and Alarm - If enabled includes for checking that the requested PV has been reached, that it has been within limits for the correct period of time and if not sets the Gua Alarm.

Properties
Class Name A unique name for this item. The class name is display only and cannot be changed.
Name Enter a meaningful name for this Item so that you, and other people, will easily recognize what it is for.
Enabled No - The ITEM is not enabled and will not update when its TASK updates

Yes - The ITEM is enabled and will update when its TASK updates.
SV at Step End Set the required Set Value for the end of the Step.
Step Time Interval Select the time interval required for this step:

Seconds, Minutes, Hours or Days.

(This property is not used in a "Slave" Step Control TASK).
Step Time Duration Select the ITEM that will set the duration of the Step. Refer Note 1.

(This property is not used in a "Slave" Step Control TASK).
Dev Alarm Enabled Enable the Deviation Alarm:

No = Alarm Disabled, Yes = Alarm Enabled
Dev Alarm Delay Select the ITEM that will set the Deviation Alarm Delay. Note that this is in the same units as the "Step Time Interval" above. If no delay is required then leave this property blank.

Refer Note 1
(Gua) Dev Hi Set the ITEM that will set the Hi deviation value for both the Guaranteed PV Alarm and the Deviation Alarm.

Refer Note 1.
(Gua) Dev Lo Set the ITEM that will set the Lo deviation value for both the Guaranteed PV Alarm and the Deviation Alarm.

Refer Note 1.
Gua Type Select the Guaranteed PV Type:

None: Guaranteed PV not enabled.

Gua PV End: Guarantees the PV only at the end of the Step. This will prevent advancing to the next Step until the PV is within limits or until the Gua Alarm - refer to "Gua Alarm Action" below.

Gua Soak Total: Guarantees the PV will be within limits for the time set by the "Step Duration" above. Refer to "Gua Alarm Action" below for options if the guaranteed time is not met.

Gua Soak Restart: Similar to "Gua Soak Total" only that this option guarantees the PV will be within limits CONTINUOUSLY for the time set by the "Step Duration" above. If at any time the PV falls outside limits then the timing will start again. Refer to "Gua Alarm Action" below for options if the guaranteed time is not met.

Gua is not used in a "Slave" Step Control TASK.
Gua Time Select the ITEM that will set the Guaranteed time, this being the time used by the Step after which the GUA Alarm is set ON.

Note that this is in the same units as the "Step Time Interval" above.

(This property is not used in a "Slave" Step Control TASK).

Refer to Note 1.
Gua Alarm Action The following are the options available should a Gua Alarm occur.

Note: For a Gua Alarm occur the "Step Time Used" must exceed the "Step Gua Time".

Wait: This option waits indefinitely for all of the conditions to be satisfied before advancing to the next Step.

Advance Step: This option automatically advances to the next Step in the event of a Gua Alarm.

Stop: This option stops the Step Control, setting the SV to the End SV of the last Step.

(This property is not used in a "Slave" Step Control TASK).
Fixed SV (No Ramp) Select an ITEM to determine if this Step will Ramp the Set Value or not. If the ITEM's value is 0 then the SV will ramp, if the value is 1 then the SV will not ramp. If nothing is selected then this property is ignored and the SV will ramp.

  

Notes

  1. All properties that reference other ITEMS do so for flexibility. The other ITEMS may be fixed values using the Math Value ITEM, or they may be variable by using say the In Input Tag ITEM which could be reading data which can be changed by an operator via the Mimic program.

 

 Refer to Step Master

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