Oldham OLCT 200 User Manual page 18

and wire sizes may be smaller. However, only very low power applications are eligible
for such transmitters. The OLCT 200 Display assembly shown in Figure 2-4 consumes
<2.5 mA of quiescent current. Toxic and oxygen electrochemical sensors generate
their own signals and therefore require no additional current. If a 4-20mA output is all
that is required for toxic / oxygen measurements (no LCD backlight, alarms or RS-485)
the OLCT 200 may be used in the 2-wire mode.
CAUTION: It is important to understand the receiver, or controller device must supply
the loop power in 2-wire 4-20mA modes. Be sure the receiver to be used supports this
type of operation.
Instructions:
Unscrew the cover on the OLCT 200 explosion-proof enclosure. Loosen the 2
thumbscrews holding the display assembly in place and remove it. A small sensor
cable is attached with sufficient length to allow access to the back of the display
assembly where 2 position TB1 is located. Route the receiver wires through the
conduit entry and connect to TB1. Steering diodes in the OLCT 200 2-wire 4-20mA
output automatically correct for polarity so positive and negative are interchangeable.
Reassemble the OLCT 200. Follow the procedures and recommendations in the
receiver manual to complete the installation. Be sure the OLCT 200 enclosure and
conduit are properly grounded. Apply loop power by appropriately powering the
receiver device (DCS, PLC, Controller, etc) and the OLCT 200 should function.
Proceed to section-3.
Figure 2-4: 10-0232 Display / 2-Wire 4-20mA Assembly
OLCT 200 User Manual | 18