How do I wire the One
Series 2-Wire electronic switch?
Is the One Series
2-Wire a “loop powered” device?
Can I use the One
Series to switch AC voltage loads?
What happens when the
set point is reached and the switch output changes state?
Will the One Series
2-Wire only work with PLCs?
Which applications
provide the best fit for the One Series 2-Wire?
Will the One Series
2-Wire fit into Intrinsically Safe (IS) applications? What about explosion
proof applications?
Does UE provide an
IS barrier for the One Series 2-Wire?
What happened to the
bright red IAW® LED from the front of the One Series?
What other features
have been added to the One Series product line?
If I need a 4-20 mA
output, can I get it with the One Series 2-Wire?
Can I use an external
power supply with the One Series 2-Wire?
How does the Plugged Port feature work?
Can the One Series be calibrated in the field?
Is the 4-20 mA output on model 2WLP and 8W2D field scalable?
How do I wire the One Series 2-Wire electronic switch?
Power
to and switched output from the One Series 2-Wire is provided
over the same wire pair. Only two wires
are required for both power and output. The electronic switch derives
its operating power from the load circuit it is driving (PLC or DCS discrete
input), much like a proximity switch. Model 2W2D draws about 400 mA from the input when
the internal switch is open and a maximum of 40 mA when the switch closes.
Model 2W3A draws about 1 mA from the input when the internal switch is open and
a maximum of 100 mA when the switch closes.
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Is the One Series 2-Wire a “loop powered” device?
Models
2W2D and 2W3A are discrete input powered devices. They utilize a small amount of leakage current derived from the
discrete input of a PLC or DCS. Model
2WLP is, in fact, a true
loop-powered version of the One Series.
This model connects to the analog input of a PLC or DCS, where a small
amount of current is derived to provide power and return a 4-20 mA proportional
signal.
How does it work?
The
One Series 2-Wire requires very little current to operate, down in the
micro-amp range. This enables the
electronics to derive power from the residual current of a typical PLC digital
input or other load (e.g., a relay coil or DCS input) without triggering the
input circuit. When the switch contact closes, only then does the input detect
a closed switch condition. By virtue of its extremely low power requirement,
the One Series 2-Wire is able to take advantage the on-off input thresholds associated
with discrete input PLCs and DCSs.
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Can I use the One Series to switch AC voltage loads?
Yes. Model 2W3A is designed to work with 115 VAC
discrete PLC or DCS inputs. Just like
the 2W2D (24 VDC) model, the 2W3A gets its power from the 115 VAC input and
provides a switch to the same input over a 2 wire connection. This model can sink or source up to 100
mA. The input voltage range for One
Series model 2W3A is 90-130 VAC or VDC, so it can operate in DC circuits in
addition to AC circuits. Model 4W3A is
a high-capacity version of the 2W3A, but requires an external power source of
90-130 VAC. The integral solid-state
relay can handle 24-280 VAC @ 10 A!
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What happens when the set point is reached and the switch
output changes state?
This
depends on how the One Series was programmed during installation. The One
Series can be set in a 2-state (on-off) or a 3-state (on-pulse-off) mode. In a 2-state mode, the One Series internal
switch will change from normally closed (on) to open (off) at set point. This is the default mode when the One Series
is shipped. The switch action can be
reversed so that the change is from normally open to closed at set point. This normally open mode is not recommended
because the One Series is a fail-safe open design, so there would be no
difference between normally open and One Series failure. In a 3-state mode, the One Series is
normally closed to indicate that the switch is functioning properly and the set
point has not been reached. At set point, rather than opening the switch, the
One Series pulses the switch (on-off rapidly) to indicate a properly
functioning switch that is alarming. If
a failure occurs or a wire connection is broken, only then will the One Series
switch open. It may be necessary to
program the PLC to accept the One Series pulses and the ladder logic code is
supplied in the One Series I&M.
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Will the One Series 2-Wire only work with PLCs?
While
PLC applications are proving to be the most popular, the One Series 2W2D and
2W3A will work with many DCS or PC discrete inputs, interposing relays,
solenoids, enunciator panels and other devices where a switch closure is
providing an alarm signal. Care must be taken to avoid exceeding the maximum
switch ratings when using loads other than the PLC or DCS discrete input.
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Which applications provide the best fit for the One Series
2-Wire?
The
One Series 2-Wire is intended for plant upgrade applications by replacing
mechanical switches and analog transmitters with the latest digital switch
technology, utilizing existing wiring and discrete input channels. In most
cases, the One Series 2-Wire will be a direct, drop-in replacement for existing
pressure and temperature instrumentation, providing a very easy and cost-effective
means to upgrade field instrumentation within a plant.
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Will the One Series 2-Wire fit into Intrinsically Safe (IS)
applications? What about explosion
proof applications?
Yes. By virtue of its extremely low power
consumption, the One Series 2-Wire is approved for Class I, Division 1
Intrinsic Safety (IS) applications when used with an appropriate IS
barrier. In many applications, IS
instruments satisfy the need for explosion proof environments when used with a
barrier. The One Series 2-Wire does not
incorporate an explosion proof enclosure or certification at this time.
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Does UE
provide an IS barrier for the One Series 2-Wire?
Yes. Product option M036 provides a
transformer-isolated safety barrier designed specifically for the One Series
2-Wire (model 2W2D only) in the same shipping carton or from UE and its
distributors using UE part number 62169-29.
The barrier is also available directly from MTL (the manufacturer) and its
distributors as part number MTL 5012S.
Regardless of where the barrier is sourced, the list price is $198
(USD).
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What happened to the bright red IAW® LED from the
front of the One Series?
The
popular I Am Working (IAW®) self-diagnostics technology is included in the One Series 2-Wire,
but is implemented differently. Due to
power restrictions in Intrinsically Safe designs, the LED (light emitting
diode) was replaced by a LCD (liquid crystal display) for local indication,
which requires much less current.
Additionally, the remote IAW® signal is incorporated into the switched output using a
pulsed pattern, providing switch and health validity and integrity information
over the same 2 wires. No additional
wiring is necessary. The One Series D1
and D2 models still include the red IAW® LED.
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What other features have been added to the One Series
product line?
The
One Series 2-Wire models include a large, easy-to-read LCD readout for display
of the process variable, switch settings, health and process extremes
values. Programming is accomplished
with a 2-button keypad. New
programmable features include Plugged Port Detection, Zero Offset and Span
Adjust, Latching Output and Event Filtering.
The 2WLP model adds field-scaling capability for the 4-20 mA output. The
keypad incorporates a key sequence to enable saving programming changes,
providing tamper resistance. The One
Series 2-Wire sensors incorporate an all stainless steel and welded diaphragms
for excellent media compatibility.
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If I need a 4-20 mA output, can I get it with the One Series
2-Wire?
Yes.
Model 2WLP provides a loop-powered transmitter version of the One Series. With a simple 2-wire connection to the
analog input of a PLC or DCS, model 2WLP provides a field-scalable digital
indicating 4-20 mA signal with 0.5% accuracy.
Model 2WLP also incorporates an auxiliary solid-state relay that
requires 2 additional wires, if used.
Power for the transmitter and the switch is provided by the analog loop.
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Can I use an external power supply with the One Series
2-Wire?
No. The One Series 2-Wire is intended for the
input of a PLC or DCS where it derives its power and provides a switch. The One Series 4W3A model accepts 115 VAC as
its power supply and provides a 24-280 VAC @ 10 A solid-state relay
switch. This model requires a 4-wire
connection.
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How does the
Plugged Port feature work?
The
One Series 2-Wire can be programmed to sense media fluctuations over a period
of time. If these “normal” media
fluctuations cease in the time allotted, it is assumed that the sensor is
clogged and unable to sense any pressure changes. The local LCD display will read “PLUG” and the switched output
will open, indicating this fault condition remotely.
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Can the One
Series be calibrated in the field?
Yes.
Adjustments for Offset and Span are included in the Advanced Features section
of the software. These commands provide ±10% adjustability over of the sensor's
range. When used, the LCD display shows an "OFFSET" icon as a warning
that significant pressure may be present even though the display is reading
zero. Entering zeros in the Offset and
Span commands returns the unit to factory settings and calibration.
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Is the 4-20 mA output on model 2WLP and 8W2D field scalable?
Yes.
There are two independent commands used to scale the 4-20 mA output in the
field - 4mA and 20mA. By entering
values using the calibrated units of measure, the 4 mA portion of the signal
can be adjusted over a range of -3% to 25%.
The 20 mA portion of the signal can be adjusted over a range of 50 to
110%. Scaling the 4-20 mA signal to
cover a smaller (<100%) portion of the sensor's range does not increase the
accuracy of the 4-20 mA signal.
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