For Sales and Support, Contact Walker EMD • Toll-free: (800) 876-4444 • Tel: (203) 426-7700 • Fax: (203) 426-7800 • www.walkeremd.com
5
POWER-UP DIAGNOSTICS
The Libra counters have internal diagnostics which will check the stored data
during power-up. When the data is saved (power-down), computations are
made with these values. The result of these computations is stored in the
memory to serve as a check against possible error. Then on power-up, these
same computations are repeated on the stored data. If these results do not agree
with the stored results, then a “P” will appear on the right side of the display.
Normal operation of the unit will continue while this “P” is displayed. To
remove the “P” from the display, press the “E” button. Then check
programmed values to be certain they are correct.
TO ENTER A DECIMAL POINT INTO THE
DISPLAY
FIRST: Press the button located under the right-hand digit. At this time, the
display will “freeze”. (The display will remain “frozen” approximately 5
seconds after release of this button,if no other buttons are pushed.) During
the selection of decimal point, the unit will operate normally.
SECOND: Press the button located under the desired decimal point location.
(The decimal point will appear to the right of the digit.) (This selection
cannot be made when “PGM. DIS.” is activated.) Pressing the button located
under the right-hand digit will display no decimal point. (This will turn off
any displayed decimal point.) After the second button pushing operation, the
unit goes back to normal display mode.
CONNECTIONS
As depicted in the drawing
showing the rear view of the Libra
Counter, there are two terminal
blocks where all wiring connections
are made. All conductors should
meet voltage and current ratings
for each terminal. Also, cabling
should conform to appropriate
standards of good installation,
local codes and regulations. It is
recommended that power supplied
to the unit (AC or DC) be protected
by a fuse or circuit breaker. The
blocks can be removed for easy
access to the terminal screws. To
remove the block, pull from the
back of the block until it slides
clear of the terminal block shroud.
Caution: The terminal blocks should NOT be removed with power applied to
the unit.
All the DC power and input connections are made to the top terminal block
labeled TBA. The AC power and output connections are made to the bottom
terminal block labeled TBB. The input connections will be discussed first,
using the drawing as a guide.
(The input connections are the same for 1 or 2 preset counters.)
EMC INSTALLATION GUIDELINES
Although this unit is designed with a high degree of immunity to
ElectroMagnetic Interference (EMI), proper installation and wiring methods
must be followed to ensure compatibility in each application. The type of the
electrical noise, source or coupling method into the unit may be different for
various installations. It should be noted that the methods listed below may not
be necessary for every unit installation. In extremely high EMI environments,
additional measures may be needed. The unit becomes more immune to EMI
with fewer I/O connections. Cable length, routing and shield termination are
very important and can mean the difference between a successful installation or
a troublesome installation. Listed below are some EMC guidelines for
successful installation in an industrial environment.
1. Use shielded (screened) cables for all Signal and Control inputs. The shield
(screen) pigtail connection should be made as short as possible. The
connection point for the shield depends somewhat upon the application.
Listed below are the recommended methods of connecting the shield, in
order of their effectiveness.
a. Connect the shield only at the panel where the unit is mounted to earth
ground (protective earth).
b. Connect the shield to earth ground at both ends of the cable, usually when
the noise source frequency is above 1 MHz.
c. Connect the shield to common of the unit and leave the other end of the
shield unconnected and insulated from earth ground.
2. Never run Signal or Control cables in the same conduit or raceway with AC
power lines, conductors feeding motors, solenoids, SCR controls, and
heaters, etc. The cables should be run in metal conduit that is properly
grounded. This is especially useful in applications where cable runs are long
and portable two-way radios are used in close proximity or if the installation
is near a commercial radio transmitter.
3. Signal or Control cables within an enclosure should be routed as far away as
possible from contactors, control relays, transformers, and other noisy
components.
4. In extremely high EMI environments, the use of external EMI suppression
devices, such as ferrite suppression cores, is effective. Install them on Signal
and Control cables as close to the unit as possible. Loop the cable through the
core several times or use multiple cores on each cable for additional protection.
Install line filters on the power input cable to the unit to suppress power line
interference. Install them near the power entry point of the enclosure. The
following EMI suppression devices (or equivalent) are recommended:
Ferrite Suppression Cores for signal and control cables:
Fair-Rite # 0443167251 (RLC #FCOR0000)
TDK # ZCAT3035-1330A
Steward #28B2029-0A0
Line Filters for input power cables:
Schaffner # FN610-1/07 (RLC #LFIL0000)
Schaffner # FN670-1.8/07
Corcom #1VB3
Corcom #1VR3
Note: Reference manufacturer’s instructions when installing a line filter.
5. Long cable runs are more susceptible to EMI pickup than short cable runs.
Therefore, keep cable runs as short as possible.
6. Switching of inductive loads produces high EMI. Use of snubbers across
inductive loads suppresses EMI.
Snubbers:
RLC #SNUB0000
DC POWER AND INPUT CONNECTIONS
Terminal number 6 on TBA (the first terminal from the left), is the +12 VDC
input/output terminal. As an output this terminal is for sensor supply and can
provide up to 150 mA of current. As an input, an external 11 to 14 VDC supply
can be applied to this terminal to power the unit in the absence of AC power.
Terminal 5 is the common terminal which the common line from the sensor and
other inputs are connected. (Do NOT connect relay commons or solid-state output
commons to this point.) Terminal 4 is the count input terminal. When the signal
at this terminal is pulled low (zero volts), a count will be registered. (See Count
Input and Count Rates under the Specifications section.) Terminal number 3 is the
UP/DN terminal (Count Direction Control). When this terminal is at a high level,
the count direction is “UP”. When the terminal is grounded, the count direction
is “DOWN”. Terminal 2 is the Program Disable (PGM. DIS.) terminal. When this
terminal is at a high level, the Preset value(s) and timed output value(s) can be
changed using the front panel buttons. (Outputs can also be tested during self-test
under this condition. See Self-Test description for further details.) When terminal
2 is at a low level (connected to COMM), changing these values and testing the
outputs is no longer possible. Terminal 1 is the Remote Reset terminal. When this
terminal is at a low level (connected to COMM), the unit will reset, and the
outputs will turn off (if activated). As long as reset is low, the unit is held at reset.
AC POWER AND OUTPUT CONNECTIONS
As mentioned before, AC power and output connections are made to the
bottom terminal block, labeled TBB. Primary A.C. power is connected to
terminal 1 and 2 (marked A.C. Power, located on the left-hand side of terminal
block TBB). For best results, the A.C. Power should be relatively “clean” and
within the specified ±10% variation limits. Drawing power from heavily
loaded circuits or from circuits that also power loads that cycle on and off,
should be avoided.
Terminals 3, 4, and 5 are used to connect to the output relay 1. Terminal 3 is
the normally closed contact. Terminal 4 is the normally open contact. Terminal
5 is the output relay common. Terminal 6 is an output common used for the
solid-state output(s). This terminal should NOT be used as the common for the
output relay(s) or as the common for the input or control terminals. Terminal 7
is current sinking output 1 (labeled 01-SNK.). This internally connects to an
NPN Open Collector transistor. The remaining terminals are for the dual preset
version of the Libra counter and serve the same functions as those for the single
preset unit. Terminal 8 is current sinking output 2 (labeled 02-SNK.). Terminal
9 is the normally closed contact of relay 2. Terminal 10 is the normally open
contact. Terminal 11 is the output relay common.
DASHED LINES ARE FOR 2 PRESET UNIT ONLY
LIBC-j.QXD 10/26/04 10:52 AM Page B5
To Next Page
Loading...
