Extech Instruments 96VFL

28 VFL Series User Manual v2.3 12/20
The High/Low Limit ‘span’ directly affects the size of the Proportional Band, as the Proportional
band value (‘Pb’) is set as a percentage of span (Menu 3, PID). The wider the span, the wider
the Proportional Band.
The span also sets the low and high boundaries for basic operation. For example, the setpoint
cannot be adjusted higher than the high limit or lower than the low limit settings.
11.3 Alarm Functions and Specialty Modes
ALARM FUNCTION LIST
Once a function is programmed in the ‘A1Fu’ and ‘A2Fu’ parameters (Menu 4, Options), set
the setpoint in Menu 1 (‘A1SP’ or ‘A2SP’ menu items).
‘A1FU’ / ‘A2FU’ setting
Alarm Type
Operation
No Alarms
No Alarms
Process High
alarm
Relay trips when the process (PV) exceeds the
‘AxSP’ value (Menu 1).
Process Low
alarm
Relay trips when the process (PV) falls below
the ‘AxSP’ value (Menu 1).
Deviation
High alarm
The Alarm setpoint equals the Setpoint (SV)
plus the ‘AxSP’ (Menu 1) setting. For example,
if SV = 400 and A1SP = +10 then the Alarm relay
will trip when the temperature rises above 410
o
(400 + 10 = 410).
Deviation
Low alarm
The Alarm setpoint equals the Setpoint (SV)
plus the ‘AxSP’ setting. For example, if SV = 400
and A1SP = -10 then the Alarm relay will trip
when the temperature falls below 390
o
(400 –
10 = 390).
Band High
alarm
Alarm trips when PV is higher than the setpoint
band.
Band Low
alarm
Alarm trips when PV is lower than the setpoint
band.
ON-Timer
See dedicated ON/OFF Alarm Timer section.
OFF-Timer
See dedicated ON/OFF Alarm Timer section.
NOTE: The complete parameter table above is listed twice in the AxFu programming menus,
with the second set reversing the alarm relay logic (normally closed, which is Form B, instead
of normally open, which is Form A) . The second set has a ‘b’ (for Form B) at the beginning of
the menu item name (‘b.Hi’, for example). See the alarm logic relay illustrations below.