7
SENSOR
INFORMATION
(tuning
fork)
Step
Three
Maintenance
Alarm
(LTU
‐
101A
series
Tuning
Fork
only):
For
optimum
performance
and
proactive
maintenance,
the
sensor
automatically
adjusts
for
coating,
and
if
necessary,
outputs
a
preventative
maintenance
alarm.
The
Yellow
wire
is
a
NPN
transistor
designed
to
switch
when
a
build
‐
up
of
material
prevents
the
tuning
fork
switch
from
operating
at
its
operational
frequency.
Use
the
Yellow
wire
to
identify
when
the
Tuning
Fork
switch
requires
cleaning.
To
wire
the
maintenance
output
wire
to
an
LED,
follow
the
wiring
diagram
below.
The
Yellow
wire
is
connected
to
the
LED
and
a
2.2k
Ω
resistor
in
series
and
referenced
back
to
the
(+)
of
the
power
supply.
Sensor
Power
[RED
&
BLK
wires]
/
36
VDC
Max.
8
±1mA
Dry
/
22
±1mA
Wet
Relay
Rating
[GRN
&
WHT
wires]
/
60
VA
Maintenance
Alarm
[YEL
wire]
/
NPN
Transistor
/
10mA
Max.
To
wire
the
maintenance
output
wire
to
a
PLC,
follow
the
wiring
diagram
below.
The
Yellow
wire
is
connected
to
the
PLC
input
with
a
10
k
Ω
resistor
parallel
to
the
PLC
input
and
the
(+)
of
the
power
supply.
Sensor
Power
[RED
&
BLK
wires]
/
36
VDC
Max.
8
±1mA
Dry
/
22
±1mA
Wet
Relay
Rating
[GRN
&
WHT
wires]
/
60
VA
Maintenance
Alarm
[YEL
wire]
/
NPN
Transistor
/
10mA
Max.