46 February 2017
SSR, and Figure 2 shows the simplified circuitry that
might be found in a typical AC SSR. The protective
part of both SSRs is the optical isolator shown on
the control or input lines of these devices. All the
controlling or input side of the circuit basically does
is energize an LED — often an infrared LED to
prevent interference from visible light — which, in
turn, shines on the base of a photo transistor.
Therefore, the only connection between the load
circuit and the control circuit is a beam of light.
This can protect your controlling circuit from
voltage levels into the thousands of volts in some SSRs
( 2,500V on the two SSRs shown in Photos 1 and 2). If
there is a problem, the SSR may be destroyed in the
process, but hopefully no damage will get back into the
In order to control either a DC or AC load with the
MyRIO, a change will have to be made to the demo VI
we have been working with in the past two articles. Open
up the final demo VI from the second article. On the
block diagram, place a digital output as shown in Figure 3;
Functions > myRIO > Digital Output. When placing
the digital output on the block diagram, another
window will appear as in Figure 4.
A configuration tab and pull-down menu will
allow you to see all 40 digital I/O lines available; we
just need the first one at this time: A/DIO0 (pin 11).
This will let our VI output to MXP port A DIO 0.
Wire the digital output in parallel with the other
outputs as shown in Figure 3. It’s always a good idea
to have your VI shut things off when closing, so copy
and paste this icon into the last frame of the VI as
shown in Figure 5; ctrl C/ctrl V will work for this.
Make sure that the closing frame icon has a constant
“F” wired to it so that it will turn off DIO 0 when the
VI is closed.
To see if this output will work, you can test it by
connecting the anode of an LED to output DIO 0 in
series with a 220 ohm resistor to ground on the MXP