Chapter Four: Functional Overview The [TRIP POINTS] Ke
57
Hysteresis Screen
TP A Hysters: 10.00%
TP B Hysters: -10.00%
The hysteresis feature, built into the operation of the two trip points, helps to compensate for the
noise inherent in all systems. Excessive noise can cause the trip points to repeatedly switch
states, a condition known as “relay chatter.”
The hysteresis value is defined as a
±
percent of the trip point entry, on the selected range. The
entry can range from 0 to 10 %. For example, if TP A HIGH is set to 70 and TP A LOW is set
for 50, a hysteresis value to 1%, will create a hysteresis band from 63 to 77 around TP A HIGH,
and a hysteresis band from 45 to 55 around TP A LOW.
Relay State
You select the state of the relays in the normal operating range, either energized or de-energized.
The relay changes state when the pressure reading on the relay channel exceeds the trip point
high value
plus
hysteresis value, or drops below the trip point low value minus hysteresis value.
For example, if TP A is set as de-energized, it becomes energized when the pressure exceeds the
range defined by the trip point values plus the hysteresis value.
Table 15: Action of the Trip
Points
, on page 54, describes the action of the trip points based on the pressure reading of the trip
point channel.
The relay state entry does not effect the function of the trip point LEDs. The LEDs always
illuminate when the pressure reading deviates from the boundaries defined by the trip point high
value plus hysteresis, and the trip point low value minus hysteresis. The LEDs are extinguished
when the pressure reading is within the trip point boundaries.
Relay State Screen
TP A ENERGIZED
TP B DE-ENERGIZED
This screen determines the state of the trip points when the pressure is between the high and low
trip point values. Set the state as either energized or de-energized. Use the Adjust knob to toggle
between ENERGIZED and DE-ENERGIZED. Use the arrow keys to move from one trip point
to the other.
The initial value is ENERGIZED for both trip points.
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