Red Lion LDSG - Manual (Page 4)

4
3.4 INPUT WIRING
3.2 USER INPUT WIRING
CAUTION: Analog common is NOT isolated from user input
common. In order to preserve the safety of the meter application,
the DC common must be suitably isolated from hazardous live
earth referenced voltage; or input common must be at protective
earth ground potential. If not, hazardous voltage may be present
at the User Input and Input Common terminals. Appropriate
considerations must then be given to the potential of the input
common with respect to earth ground. Always connect the
analog signal common to terminal 4 (-EXC).
The User Input is located: LD2 - left side, LD4 - right side
Terminal 1: User Comm
Terminal 2: User 1
Terminal 3: User 2
Terminal 4: User 3
3.3 SETPOINT (OUTPUT) WIRING
The setpoint relays use a six position terminal block (TBB) located inside the
(right side).
Terminal 1: NC 1
Terminal 2: NO 1
Terminal 3: Relay 1 Common
Terminal 4: NC 2
Terminal 5: NO 2
Terminal 6: Relay 2 Common
USER *
USER COMM 1
TBD
USER
USER COMM 1
*
TBD
+
-
1 N.C. 1
COMM 1 3
2 N.O. 1
TBB
4
5
6
N.C. 2
N.O. 2
COMM 2
Sinking Logic
Sourcing Logic
2
1
4
3
+EXC
+IN
-IN
-EXC
TBC
EXC+
EXC-
SIG-
SIG+
RS485 Communications
The RS485 communication standard allows the connection of up to 32 devices
on a single pair of wires, distances up to 4,000 ft. and data rates as high as 19.2K
baud. The same pair of wires is used to both transmit and receive data. RS485
is therefore always half-duplex, that is, data cannot be received and transmitted
simultaneously.
RS232 Communications
RS232 is intended to allow two devices to communicate over distances up to
50 feet. Data Terminal Equipment (DTE) transmits data on the Transmitted Data
(TXD) line and receives data on the Received Data (RXD) line. Data Computer
Equipment (DCE) receives data on the TXD line and transmits data on the RXD
line. The LD emulates a DTE. If the other device connected to the meter also
emulates a DTE, the TXD and RXD lines must be interchanged for
communications to take place. This is known as a null modem connection. Most
printers emulate a DCE device while most computers emulate a DTE device.
Some devices cannot accept more than two or three characters in succession
without a pause in between. In these cases, the meter employs a busy function.
As the meter begins to transmit data, the RXD line (RS232) is monitored to
determine if the receiving device is “busy”. The receiving device asserts that it
is busy by setting the RXD line to a space condition (logic 0). The meter then
suspends transmission until the RXD line is released by the receiving device.
5
LD METER RECEIVING DEVICE
+3.3V
4
47K
47K
3
B (-)
A (+)
COMM.*
Transmit
Enable
* OPTIONAL
Terminal Block Connection Figure (RS485)
1
2
3
Terminal Block Connection Figure (RS232)
3.5 SERIAL WIRING
TBE
A
COMM
RXD
TXD
4
2
3
1
B 5
232
485
The serial connections are made via terminal block TBE located inside the
unit on the left side for the LD2 and on the right side for the LD4.
Before connecting signal wires, the Range and Excitation Jumpers should be
verified for proper position.
* For single ended input, tie terminal 3 (-IN) to Terminal 4 (-EXC).