Hello - this is my first post here so please don't bite!
I've started a job recently as a PLC/SCADA system programmer and have been left to work out quite a lot of things for myself. I've come across a piece of (hopefully) basic electronics I don't understand and was hoping someone could explain it or point me to a useful resource.
I am working with a PLC that comes equipped with 2 transistor switched outputs and a number of relay switched outputs. I understand the relay switches - two wires needed to the load, one "in" and one "out" of the PLC to form a circuit.
I am struggling to understand the transistor switch output - it has three terminals for its output. My understanding is that I should only see two - the collector and emitter, which has a power supply in line with the load (like the relay switch outputs). The terminals are labeled V0+, V0- and 0.
If I wire this up according to the PLC instructions the LED lights up brightly as expected. If I bypass the seemingly superfluous V0- connection the LED still lights up but is dimmer. I am struggling to understand the need for this extra connection and what it does, as it seems to go a step beyond a simple transistor-LED circuit. My wiring methods are shown in bmp attachments LED1 and LED2.
Also, a wiring schematic for the transistor output from the PLC's online manual is attached.
If anyone can point me to a site that explains this circuit type or point out why the system is designed and works properly with the third terminal it would be of great help.
SheffGruff.
I've started a job recently as a PLC/SCADA system programmer and have been left to work out quite a lot of things for myself. I've come across a piece of (hopefully) basic electronics I don't understand and was hoping someone could explain it or point me to a useful resource.
I am working with a PLC that comes equipped with 2 transistor switched outputs and a number of relay switched outputs. I understand the relay switches - two wires needed to the load, one "in" and one "out" of the PLC to form a circuit.
I am struggling to understand the transistor switch output - it has three terminals for its output. My understanding is that I should only see two - the collector and emitter, which has a power supply in line with the load (like the relay switch outputs). The terminals are labeled V0+, V0- and 0.
If I wire this up according to the PLC instructions the LED lights up brightly as expected. If I bypass the seemingly superfluous V0- connection the LED still lights up but is dimmer. I am struggling to understand the need for this extra connection and what it does, as it seems to go a step beyond a simple transistor-LED circuit. My wiring methods are shown in bmp attachments LED1 and LED2.
Also, a wiring schematic for the transistor output from the PLC's online manual is attached.
If anyone can point me to a site that explains this circuit type or point out why the system is designed and works properly with the third terminal it would be of great help.
SheffGruff.
