Maple Systems OIT Family (ASCII) User Manual

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verted to 34ºF. Technically, this is inaccurate since 1ºC = 33.8ºF. Fortunately, this can

be corrected by simply using a different formula. If the conversion accuracy must be to

one decimal point, then multiply the given equation on the left hand side by 10 (for ex-

ample, Y=(90/5)X+320) and select a decimal point of 1 for the register monitor dis-

play. Finally, the above formulas will only work if the Celsius temperature values

stored in the OIT register are always integer whole number values. If the Celsius tem-

perature values in the OIT register are to one decimal point and the Fahrenheit tempera-

ture values are to be displayed to one decimal point, the following formula should be

used (Y=(9/5)X+320).

Set Points

Each OIT has a maximum of 16 set points that can be active simultaneously. The system pro-

grammer provides the following information about each:

•

OIT register address to monitor (known as set point address)

•

Format of OIT register (Signed, Decimal, 4-Digit BCD, 8-Digit BCD, or Long)

•

Low limit

•

High limit

•

Screen number to display upon low limit violation

•

Screen number to display upon high limit violation

Set points may be used for a variety of things including system warnings or alarms, multi-point

warnings or alarms, restarting a recipe after a given number of units have been batch processed,

or providing the OIT operator with a choice of actions when a trip point has been exceeded.

The set point addresses are monitored continuously by the OIT. The OIT will poll one of the

set point addresses every second. Therefore, more set points means that each particular set

point will have a longer interval of time before it is polled again (example: having 16 set

points means each set point will be polled every 16 seconds). If the OIT determines that the

current value in the set point register is below the low limit or above the high limit, then the

appropriate screen is displayed on the OIT. The screen displayed can be an alarm, message,

recipe, or menu.

Once an out-of-range condition has occurred, the set point screens cannot be activated again

until the set point address value comes back into range. For example, suppose a set point has

been configured to monitor OIT data register address D0. The set point is configured to dis-

play Screen #1 if D0 falls below -100 and Screen #2 if D0 rises above +100. The OIT data

ceeded) causing the OIT to display Screen #1. From now on, the OIT will not display Screen

#1 or #2 until D0 goes back into range: -100 to +100. Therefore, if D0 were to change from

-200 to +300, then Screen #2 would not be displayed. However, if D0 were to change from

-200 to 10, then to +300, Screen #2 would be displayed.

Note: Depending on the poll rate (number of set points), data may change many times before

being detected by the OIT.

The set points are monitored continuously by the OIT. Due to the polling interval time, if the

set points are used as alarms, they should be treated as auxiliary alarms and placed at priori-

ties 3 and 4 while the ASCII host generated alarms are placed at priorities 1 and 2.

Note: Under no circumstances should set points be used to monitor safety critical processes or limits!

FEATURES

1010-0088, REV02