Rice Lake RD-300 Remote Display - Manual (Page 10)

8 RD-300/RD-232 Installation & Operation Manual
2.4 Serial Data Inputs
The RD-300/RD-232 can accept serial ASCII data sent in RS-232C, or 20 mA active or passive current loop
formats. To select an RS-232 input signal, Set SW2-8 OFF. To use any current loop signal, set SW2-8 ON. See
Figure 2-4. These formats determine the electrical way that data is transmitted. This has nothing to do with what
data is sent.
Figure 2-4. Switch Setting SW-2
The RD-300/RD-232 can read the data transmission strings sent by 15 of the more popular scale indicator
families. It cannot read data from meters not included in this list unless you use universal mode or the formatting
exactly matches one on the list (or you have a custom program). Set up the RD-300 on the bench with the meter
you intend to use before taking it to the installation site.
Some indicators are built with their RS-232 serial port signal ground combined with the general chassis
ground. When the RD-300 or RD-232 Remote Displays are connected to such an indicator sending RS-232, half of the power
supply is being shorted to chassis ground via the offending RS-232 signal ground connection. The result is extreme heat in the
transformer and premature failure.
With Analogic indicators and other products combining RS-232 signal ground and chassis ground, do not use RS-232 output.
Set both the indicator output and the remote display input to 20 mA current loop instead.
Check your indicator’s electrical schematics—or feel for extreme heat at the RD-300/RD-232 transformer—to determine if your
indicator has a combined RS-232 signal and chassis ground. If so, use 20 mA current loop.
2.4.1 RS-232 C - SW2-8 Off
Data is transmitted as a voltage and alternates between
+10 VDC and -11 VDC. Hybrid “RS-232” signals
can swing between other voltage ranges as long as the
positive swing is greater than 4 VDC and the negative
is less than -1VDC. RS-232 is ground referenced and
therefore, connects the ground planes of the sending
and receiving instruments. RS-232 should never be
run more than 50'. It may work, but it may not work
well all the time. Long RS-232 data cables can act as
a conduit for lightning or other electrical noise to the
instrument. If you need longer cable runs, use a 20
mA current loop. If this is not available on your
indicator, consider an optically isolated protocol
convertor to change the RS-232 to 20 mA loop and
optically isolate the ground planes of the two
instruments.
Connect RS-232 wiring as shown in Figure 2-5
(RS-232, GND). Strip the wires approximately 3/16".
Press on the white lever to open the connector. Insert
the wire and release the lever. Test the tightness by
gently pulling on the wires. Tighten the strain relief
fitting around the RS-232 cable with a wrench or
pliers.
Figure 2-5. RS-232 Wiring Assignment








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