Rice Lake EL232 XPCD Explosion Proof Remote Serial Display - Manual (Page 19)

Indicator Setup 15
Connect RS232 wiring as shown in Figure 3-5. Strip the wires approximately 3/16" and insert them into the
connectors as shown. Tighten the connectors and test the tightness by gently pulling on the wires.
Figure 3-5. RS232 C Input Hookup
The RS232 receiver in the EL232 XPCD is made from discrete components and requires a lower current than
most integrated circuit RS232 receivers. It is very difficult to damage and holds up under most conditions.
3.2.2 20 mA Active Current Loop Input
Data is transmitted as a current and is passed through an optical isolator. This current causes an LED to emit light
onto a photo transistor, which converts this light into a TTL signal. Current transmission can be made over long
distances and are quite immune from transient voltage or RFI/EMI noise. The distance a current loop can
transmit is limited by the voltage source available to the current loop and the speed of transmission which data is
sent. Normally a current loop should not send data at speeds greater than 4800 baud.
An active current loop means that the instrument which sends the data also supplies the voltage to power the
loop. This voltage can be as small as 5 VDC to as much as 24 VDC. When the loop goes through an optocoupler,
a drop occurs. This drop is about 2 VDC. A current loop can power as many drops as there is voltage to power the
loop. For example, if a current loop is powered by 5 VDC, it can normally drive two drops. If the same loop were
powered by 24 VDC, it could power about 11 remote displays or other devices.
Determine that your indicator has an active current loop and connect it as shown in Figure 3-6. Strip the wires
approximately 3/16" and insert them into the connector as shown. Tighten the connectors and test the tightness
by gently pulling on the wires.
Figure 3-6. 20 mA Active Current Loop Input Hookup
The 20 mA receiver in the EL232 XPCD is a HP-4200 and requires current swings of less than 4 mA as a mark
and greater than 12 mA for a space. The output of the HP-4200 is a TTL signal which appears at pin #7 of the
chip.
GND PRINT K4 K3 K2 K1 +5V CL4 IN- CL4 IN+ CL3 IN- CL3 IN+ CL2 IN- CL2 IN+ CL1 IN- CL1 IN+ CLO OUT
-
CLO OUT+
J2
RS232 (+) GROUND
GND PRINT K4 K3 K2 K1 +5V CL4 IN- CL4 IN+ CL3 IN- CL3 IN+ CL2 IN- CL2 IN+ CLO OUT
-
CLO OUT+
J2
CL (+) CL (-)
RS-232 (+) RS-232 (-)