<5. Functions>
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IM 01E21A02-03EN
5.3 Limit Switch Function
5.3.1 Limit Switch
The limit switch function is to transmit 0 and 1 as a parameter by judging whether the selected
process value is above or below the threshold value. The function operates as the figure below.
State 1
State 0
F0447.ai
Active direction: Low limit
Set point + Hysteresis
Set point
Output
Process value
Time
Active direction: High limit
Set point
Set point - Hysteresis
Output
Process value
Time
State 1
State 0
Figure 5.3.1 Limit Switch Operational Schematic Figure
Function item
Description of Parameter
Operation
direction
Specifies the operation direction of the limit switch.
0 Low limit
1 High limit
Threshold
Specifies the threshold for judgment.
Hysteresis
Specifies the hysteresis (only a positive value can be specified).
Contact point
output
0 (State 0) or 1 (State 1) is entered.
Figure 5.3.1 shows examples of the operation for a case where the operation direction is Low
limit on the left side and a case where the operation direction is High limit on the right side.
When the operation direction is Low limit, a contact point output becomes 1 (State 1) if the
process value goes below the threshold. When the process value goes over the value obtained
by adding the hysteresis to the threshold (thr hysteresis) after that, the contact point
output becomes 0.
When the operation direction is High limit, the operation is opposite to the operation for Low
limit. When process value goes over the threshold, the contact point output becomes 1 (State
1). When the process value goes below the value obtained by deducting the threshold from the
hysteresis (threshold - hysteresis), the contact point output becomes 0.
On this product, two units of the above parameter and process value unit are prepared for each
process value. Meanwhile, the value of contact point output is updated only when selected by the
channel of the DI function block.
Flow velocity limit switch
Display
--
F
OUNDATION
Fieldbus
Device Configuration ► STB ► Device Configuration ► Configuration ►Limit Sts Velocity
► (see below)
Block
Name
Relative
Index
Parameter
Description
Display
F
OUNDATION
Fieldbus
STB
108
--
Limit Sts Velocity1 Value ►
Lmt Sts Velo1.Status
Displays the status of the contact point
output of flow velocity limit switch 1.
STB
--
Limit Sts Velocity1 Value ►
Lmt Sts Velo1.Value
Displays the contact point output of flow
velocity limit switch 1.
