Emerson 3200 Installation, Operation And Maintenance Instructions - Page 7
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YARWAY 3200 ELECTRONIC WATER LEVEL GAUGE
INSTALLATION, OPERATION AND MAINTENANCE INSTRUCTIONS
5.4 Electronic Fault
The Yarway 3200 is equipped with a fault-
annunciating relay that monitors critical
internal electronic circuitry. The fault relay
is energized and the output contact is closed
when no faults are present. If the supply power
to the device is lost or if one of the conditions
listed below were to occur the fault relay would
de-energize and the fault contact would open.
5.4.1 Power Supply Fault
Two separate power supplies (PS1 and PS2)
provide logic power for the Yarway 3200. The
output of both power supplies is diode shared
such that if one supply fails, the remaining
supply will carry 100% of the system load.
CAUTION
Make sure the supply power is isolated before
replacing the fuse.
Each supply has a full bridge rectifier, filter and
12-volt voltage rectifier. The two DC supplies
share a low voltage transformer with fused
input. If a fault were to occur within any part of
this circuit the fault circuit would de-energize
the fault relay and turn on the PS1 or PS2 LED
to indicate the fault area.
If both supplies fail, check the fuse. This can
be accomplished by removal of the cover and
faceplate of the module, which will expose the
fuse.
For 120 V AC systems replace with 1/2 A 250 V
2AG fast acting subminiature fuse, similar
to Littelfuse 225.500. For 240 V AC systems
replace with 1/4 A 250 V 2AG slow acting
subminiature fuse, similar to Littelfuse 229.250.
5.4.2 Clock Fault
A 1 Hz square wave is used as the timing base
for the DC detection circuit.
A failure of the clock circuit may not affect the
ability of the device to sense water; although
over the long term (3000 hours or more)
electroplating will take place. In the short term,
therefore, the failure is not serious. If a fault
does occur, the clock fault LED will turn on. The
circuit board must be replaced.
5.4.3 Optional Continuity (Open Circuit)
If two signal wires are run to each probe, a
cable continuity test can be performed. One
wire connects to the "P" (probe) terminal
and the other connects to the "C" (continuity)
terminal. The opposite ends of both are wired to
the probe. If either wire is broken, a continuity
fault occurs for that level, turning on the
appropriate light and de-energizing the fault
relay. If the break is in the wire connected to
the "C" terminal, the level will still show proper
steam/water status. If the break is in the wire
connected to the "P" terminal, the level will
always show steam.
If single wiring only is used, adding 12 wire
jumpers on the circuit board will disable the
continuity function. Connecting the "C" to the
"P" on the terminal strip will also disable this
function.
When there is a continuity discrepancy, the
continuity fault light for the corresponding
level will turn on. However, this indication will
automatically be disabled if a clock failure
occurs.
5.5 Level Error
The Yarway 3200 is also equipped with a Level
Fault relay.
The alarm relay will energize if water is shown
over steam. Probe 1 is the lowest, probe 12 is
the highest. If any probes are unused, ensure
they are the highest probes.
6 DETECTION THEORY
A symmetrical square wave with a period
of 1 second is generated in the Yarway 3200
System. This signal is input to each of the
detection circuits and, through a resistor, to the
probe field terminal blocks.
When the probe insulator and tip is immersed
in water a current path to ground is completed
and the current flow through the circuit
causes a voltage differential to appear across
a reference resistor in the electronic module.
The voltage is measured at the +VE input of
an amplifier and compared to a fixed value
at the -VE input of the same amplifier. When
the differential exceeds the fixed setting
the amplifier outputs a signal indicating the
presence of water.
One of three of these fixed settings, or
"sensitivities" is selected as explained in
Section 5.3 (a lower conductivity water is said to
require a higher "sensitivity"). Select the lowest
sensitivity that will work with your application.
The intermediate or low sensitivity settings
increase the maximum cable distance between
probe and electronic module to 165 ft (50m) and
500 ft (152m) respectively. Otherwise, the cable
distance must be limited to 65 ft (20m).
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