Schmitt Trigger Block - Mitsubishi a2 Series Programming Manual

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2 Simple Application Controllers
6.18

Schmitt Trigger Block

The Schmitt Trigger is used to compare an Input value against a specified high and low limits
thus turn the Output ON/OFF when certain conditions are met. There are three values that
must be set - the Input Value, the Low Limit and the High Limit. All three values can be either
DirectSet, Analog In, or Function Block values. When the High Limit value is larger than the
Low Limit value, the output will turn ON when the High Limit value is reached or exceeded. The
Output will turn Off when the Input value is equal to or less than the Low Limit. (The Output
does not turn OFF when the Input Value falls below the High Limit), eg. an air conditioner is set
to turn ON when the air temperature reaches 23
reaches 18
temperature fluctuations.
When the High Limit value is less than the Low Limit value, the Output ON/OFF pattern is
reversed. When the Input Value is greater than or equal to the Low Limit Value, the Output
turns OFF. When the Input Value is equal to or less than the High Limit value, the Output
comes ON. The input pin must be ON for the Function Block to register a new value from a
Function Block or Analog Input. Therefore, the input pin must be ON for the status of the
Output to change. The input pin does not have to be ON for the Output to be ON.
Table 6.19: Schmitt Trigger Function Block
Function
0 0 0
I P O
S T
°
C. The air conditioner is not constantly turning ON and OFF over slight
Set Item
I Input pin for Schmitt Trigger operation
The following conditions apply to the function block:
1) Low (compare value L)
a) DirectSet (Constant value): setting range -32768 to +32767 with
b) Analog In (Analog Input) : setting range A01 to A08 with an
c) FB Value: output value from a function block
2) Input (input value I)
a) DirectSet (Constant value): setting range -32768 to +32767 with
FB
b) Analog In (Analog Input) : setting range A01 to A08 with an
c) FB Value: output value from a function block
3) High (compare value H)
a) DirectSet (Constant value): setting range -32768 to +32767 with
b) Analog In (Analog Input) : setting range A01 to A08 with an
c) FB Value: output value from a function block
The compare instruction is only performed if the input signal is ON.
Output Status:
Output
refer to the operation time charts for schmitt trigger condition.
°
C and turn OFF when the temperature
Description
an initial value 0
initial input A01
an initial value 0
initial input A01
an initial value 0
initial input A01
Function Blocks 6
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