Using PCSDB Constants

Overview

PCSDB Constants allow the user to set a value and reuse it in expressions. If the value needs to change, the Constant value can be changed once and all the expressions will follow suit. Here are some sample expressions using PCSDB Constants.

Example

In this case this expression is used when a machine has been in unknown downtime for more than 30 seconds. If this value were used in multiple expressions and the value were to change each expression would need to be manually adjusted.

1. From the DataXchange tab, go to Variable → PCSDB Constants.
2. Create a constant named “cycleEndDelay” with a value of 30.
3. This can now be used in any expression where a cycle should not end until 30 seconds have passed. An example is below:

([PCSDB.general_equipment_status] = [PCSDB.UNKNOWN_DOWNTIME]) AND ([PCSDB.general_equipment_status_time] > 30) AND ([PCSDB.prev_general_equipment_status_time] <= 30)

Now let’s create this same expression using the constant cycleEndDelay:

([PCSDB.general_equipment_status] = [PCSDB.UNKNOWN_DOWNTIME]) AND ([PCSDB.general_equipment_status_time] > ([PCSDB.constant]{cycleEndDelay})) AND ([PCSDB.prev_general_equipment_status_time] <= ([PCSDB.constant]{cycleEndDelay}))

Because these PCSDB Constants are independent of the expression, changing the constant value of cycleEndDelay will cascade the adjustment to all machines assigned. This eliminates the steps of making the changes to each expression on each machine which is time consuming and can lead to mistakes. Additional information on expressions is available here.