Valve Types - Lennox LXTFF01M Manual

When PWM valves or fl oating servo-actuators are used the
quality of the fi nal proportional regulation is directly associated
to how accurately is performed the system tuning. When simple
on-off valves are used no proportional action can be obtained:
the relevant driving will always be either full-on or full-off, with a
differential value set on parameter P18.
In this situation both parameters "proportional band" and "integral
time" are not used.
The fan is driven in a proportional way only in case the regulator
has been set with automatic speed control. When the valve is
proportional type, the P + I regulation will provide the correct fan
speed, meanwhile in case the valve is not proportional type ,
the fan speed will be selected according to a purely proportional
(P) rule, therefore only the "proportional band" parameter will
be used to decide how reactive will need to be the fan against
variations in the room temperature.
The distance between the three speed stages is calculated
dividing by three the proportional band and rounding down. For
example if the proportional band is 2°C, the distance between
stages will be 0.6°C.

VALVE TYPES

This regulator can drive the following type of valves:
ON-OFF: if Normally Closed (NC) it enables the water fl ow when
power is applied; if Normally Open (NO) water is normally fl owing
when the valve is unpowered and is stopped when powered.
Wiring diagram in Fig. 8 a, c and e.
40
PWM: same as above; moreover the regulator
controls the water fl ow in a proportional way by driving the valve
with power pulses whose duration in time is a function of how
much heat the room is requiring (PWM).
3 point fl oating servocontrol: this is a kind of motor valve featu-
ring one "open" wire and one "close" wire, plus a common wire.
This type of valve is characterized by a nominal opening time
(defi ned by the manufacturer) whose value must be set into pa-
rameters C03 and C04. The regulator will drive this valve through
power pulses with one second resolution in a way that its stem
will reach the position needed for the regulation, thus performing
a proportional modulation.
The relevant wiring diagram is shown in Fig. 8 b, d and f. When
the thermostat is confi gured to control a 3 point valve, upon
power-up, before starting the room temperature regulation, it will
perform a valve position resynchronisation cycle. This consists
of closing the valve for a time equal to 150% of the nominal set
time. The resynchronisation cycle in progress is shown on the
display by the " " icon.
This cycle will be periodically repeated in order to recover
possible positioning errors which might be accumulated during
time.
LXTFF01M-IOM-1511