I-O Display Systems Basic I/O Product - Manual (Page 39)

Setup & Installation 2
2-22(Vol.1)
Analog outputs:
Modules should NEVER be installed or removed while power is applied to the BASIC I/O.
Following insertion in their respective sockets, modules should b secured with their captive
screw. Correct polarity is essential to proper operation.
Note: Analog modules run hot to the touch.
Both voltage and current output modules provide their own isolated power output. This
eliminates the need for external power supplies and insures electrical isolation between each
output. This also makes it possible to wire voltage outputs in series to obtain larger voltage
swings.
The wiring of analog output modules can be verified by the host issuing a configure as outputs
instruction, Setup 1, followed by a set output level analog J instruction. See software protocol
manual , or Quick reference card for instruction details.
Module status indicators for analog outputs blink briefly as outputs are updated. It should be
noted that the status indicator only follows the logic instruction to the modules and does not
show that the module or its fuse is present. Outputs can only be verified by observing the
output device or by a multimeter or oscilloscope measurement.
OI420 analog output modules provide the current into loops with total resistance less than 275
ohms. If the loop resistance exceeds 275 ohms, an external power supply must be added to the
loop as shown in figure 2-13 correct polarity is essential. The added voltage should be a
nominal 1 volt for each added 50 ohms of loop resistance in excess of 275 Ohms. The total
added voltage can be up to 5 volts larger than the nominal calculation without damage. The
voltage regulation of the added supply can be as poor as +/-10% without affecting accuracy.
Figure 2-13 Analog Voltage and Current Output Wiring