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 The
2000 Series "A" Option provides two Form C, 10-A contact
relays (250 V-AC) on a plug-in board. The "B" Option
board provides two Form A opto-isolated AC/DC solid-state relays rated 120
mA at 125 VAC or 250 mA at 150 VDC.
Both
options are available for all models, for applications that require alarms
and/or process control. The solid-state version is recommended for
high duty cycles and low-level loads.
Either
setpoint may be latching or nonlatching. In the
latching mode, when an alarm or shutdown condition is reached, the output
remains in the alarm condition until reset via front-panel push buttons,
the optional serial interface, or a logic signal
received at the rear connector. In the nonlatching mode, the output
is automatically reset as soon as the alarm condition ceases to occur.
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In
NONLATCHING operation, the relay closes when the reading rises above
the setpoint and opens when it falls below the setpoint. Relay
ON/OFF control action is independently programmable for each of the
two relays and can be reversed through a setup command. |
In
LATCHING operation, the relay stays actuated until reset
externally. This mode can be used to shut down machinery or a
process when an operating limit has been exceeded, or to maintain an
alarm until acknowledged by an operator when the alarm condition has
passed. |
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Mixed
LATCHING and NONLATCHING Relays: One of the relays can operate in a
nonlatching mode—for example, to turn off a heater when a
temperature setpoint is reached. Operating as a latching
fail-safe backup, the other relay can turn off the entire process
when a second, higher setpoint is reached (indicating a
malfunction). |
Each
relay may be separately configured to be energized above or below the
setpoint, or may be disabled. Also, each relay may operate in band
deviation or hysteresis mode.
Deviation
mode sets up a passband around the setpoint and is often used for
component pass-fail testing. In this mode, an alarm is generated
whenever the reading is a specified number of counts above or below the
setpoint—for example, to flag an out-of-tolerance condition.
In
hysteresis mode, the relay is activated at a specified amount above
the setpoint and deactivated at the same amount below the setpoint.
Hysteresis can be used to extend relay contact life by minimizing relay
chatter around a setpoint due to signal noise or feedback from load
switching.
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In
the above figure, a DEVIATION limit of 50 is set up on each side of
the setpoint. The relay closes (or opens) when the reading
falls within the deviation band, and opens (or closes) when it falls
outside this band. This mode establishes a passband around the
setpoint, and is often used for component testing. |
In
the above figure, a HYSTERESIS limit of 600 is set below the
setpoint. The relay closes when the reading reaches a lower
limit (i.e., the setpoint less hysteresis) and opens when the
reading reaches an upper limit (i.e., the setpoint). One
application of wide hysteresis is automatic tank filling. A
fill operation is automatically initiated when the tank level
reaches a lower level and is terminated when the level reaches an
upper limit |
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Hysteresis
can be used to minimize the number of ON/OFF control cycles around a
setpoint, thereby increasing the life of motors, relays, etc.
A narrow hysteresis band—such as the 5 counts shown in the above
figure—can also be used to minimize relay chatter around a setpoint
due to electrical noise on the signal, or to signal feedback caused
by load switching. In this case, the hysteresis limit should
exceed the noise amplitude. |
Relay
action may be derived from the filtered measurement signal, to
reduce the chance of alarm triggering due to noise. Or it may be
selected to operate from the unfiltered signal, to achieve the
fastest response time (typically 17 ms for a Digital Panel Meter with the
solid-state relay board).
Relay
chatter from signal noise can also be reduced by activating a programmable
time delay (1 to 128 readings, corresponding to 20 ms to 2 s) prior to
updating the output. Snubber circuitry in the relay board helps
prolong contact life. The relay response time of counter
meters is controlled by a selectable gate time from 10 ms to 199.99 s.
Dual
Controller Specifications [Top 
]
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Basic
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Power
|
Provided
by basic meter
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Update
Rate |
60 Hz or 50 Hz |
|
Setup |
Setpoint values
may be entered via front-panel push buttons or optional RS232/RS485
interface |
|
Lockouts |
Front-panel push
buttons can control both display and change of setpoints, or display of
setpoints only—or they can be completely disabled |
|
Output
Operation |
Either output may
be set to operate above, below, or around the setpoint (via band deviation
or hysteresis mode), latching or nonlatching—or it may be disabled |
|
Filtering |
Comparison to
setpoints may be either from the filtered or unfiltered input signal |
|
Time
Delay |
Selectable time
delay of output status change (from 1 to 128 readings) |
|
Hysteresis |
Selectable from 0
to +99999 counts |
|
Alarm
Status Indicators
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|
Type |
2 red LED lamps;
each lamp is lit when the corresponding relay is energized |
|
Contact
Relay Output ("A" Option)
|
|
Power
Rating |
|
AC
Load |
10 A at 250 VAC |
|
DC
Load |
8 A at 24 VDC |
|
Isolation
to Signal and Meter Ground |
|
Group |
C |
|
Rated
Voltage |
259 VAC |
|
Withstand
Voltage |
4.2 kV peak for 1
min. |
|
Response
Time to Input Signal |
|
Pickup
(for DPM) |
26 milliseconds,
typical (unfiltered) |
|
Release
(for DPM) |
22 milliseconds,
typical (unfiltered) |
|
Pickup
or Release (for Counter Meter) |
Gate time + 30 mx
+ 2 periods max. |
|
Solid-State
Relay Output ("B" Option)
|
|
Power
Rating |
|
AC
Load |
120 mA at 125 VAC,
20 Ω series resistance |
|
DC
Loads |
2 loads: 250 mA,
0-150 VDC peak holdoff, 5 Ω series resistance
4 loads: 120 mA, 0-150 VDC peak holdoff, 10 Ω series resistance |
|
Isolation
to Signal and Meter Ground |
|
Type |
Optical |
|
Safety
Rating |
250 VAC, 4.2 kV
peak per high-voltage test |
|
Response
Time to Input Signal |
|
For
DPM |
17 milliseconds,
typical (unfiltered) |
|
For
Counter Meter |
Gate time + 30 mx
+ 2 periods max. |
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