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Submitted by Galil_MarissaT on Thu, 10/11/2012 - 15:00
Optoisolated Outputs Video Screenshot

Galil has recently added a new video to its growing library of 2-minute instructional videos. This latest video gives recommendations for wiring and supply voltages when connecting to the optically isolated outputs on Galil controllers.

Galil’s latest generation controllers including the DMC-40x0 Accelera, DMC-41x3 Econo, DMC-30000 Pocket Motion Controller, and RIO Pocket PLC Series come standard with optically isolated inputs and outputs. Optical isolation prevents electrical noise, voltage spikes or shorts on I/O lines from affecting the logic circuitry. This video focuses on best practices for connecting the outputs between the controller and load, and for connecting an external power supply to assure true optical isolation is maintained. Proper connections when using the various output options such as sourcing or sinking, supply voltages, and current ratings are discussed. Techniques for by-passing the optical isolation circuitry are also presented.

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In addition, for the specific wiring diagrams and pin-outs for your controller, please find your manual here:  Product Manual and Command References


Galil's latest generation controllers come standard with optoisolated outputs. Optoisolated allows for the outputs to be electrically-isolated from the controller. One of the biggest benefits to optoisolation is that it prevents noise or voltage spikes on the output lines from effecting the controller’s internal logic. In addition, it can also act as a buffer that protects the controller from any high-voltages, shorts, or electrical damage that can occur on the output-side.

Here is a simplified wiring diagram of the sinking and sourcing options of the optoisolated outputs. In sinking or “low-side” configuration, the switch is placed between the load and ground. In sourcing or “high-side” configurations the switch is placed between the voltage supply and the load.

The optoisolator is made up of an emitting diode and an optical receiver. When current is flowing between 3.3V and ground, the diode emits light and turns the receiver switch “on;” when no current is flowing, no light is emitted and the switch is “off.” 

As required for true optoisolated, the user must supply an external voltage to provide power to the load. Galil’s optoisolated outputs can be powered by placing 5, 12, or 24 VDC on the “Output Supply” and the power supply ground to the “Output Supply Return.”

Optoisolation can also be by-passed meaning the outputs can be powered using the +5 V and GND reference on the controller. Even with an external supply, one may inadvertently by-pass optoisolation by tying the GND of the controller with the Output Supply Return.

The different current ratings also have different properties and internal switches that one should consider before ordering:  The 4mA sinking option uses a photo-transistor as the switch. The 25mA option, in comparison, uses a Darlington pair. The transistor used in the 4mA has a lower current gain and a smaller voltage drop across it; Whereas, the 25mA sink/sourcing options have a higher current gain and larger voltage drop. This results in two distinct behavioral differences between the two: First, the 4mA option will have better response time-—all though timing is usually a non-issue for digital outputs. Second, the 25mA sinking configuration may drive the voltage only as low as 1.2 VDC when the Darlington pair is saturated, this may be a concern for applications using the output for logic signaling.

The 500mA option also has it's own unique properties. All though much more complicated internally, the sinking and sourcing options are wired in the same way as the sinking and sourcing options previously shown. One of the differences, is that the switch type is an optoisolator and a MOSFET. When “off” the MOSFET acts as an open circuit, and when “on” can be thought of as a very small resistor, about .1 Ohms. Due to this property the 500mA sinking configuration drives the output voltage essentially to 0 VDC, an advantage over the 25mA option. Another important distinction is that the high sourcing option has a minimum supply voltage of +12V so it cannot be powered using the + 5V reference of the controller.

Here is a summary of the latest generation of Galil products and the various optoisolated options and defaults of each.

For more information on opto-isoalted outputs, please refer to the user manual for your specific controller or call an Applications engineer!