This measurement column addresses frequently asked questions received by our customer support center and provides answers to those questions.
We frequently receive inquiries about wiring PLC counter units and rotation speed indicators when the pulse signal output from a rotary encoder is an open collector output.
This time, we will mainly explain the flow of electric current.
If it's a voltage signal, you can easily imagine wiring it to the PLC's input + and -, but the question arises as to what happens in the case of an open collector, which is not a voltage output.
An open collector is easier to understand if you think of it as an ON/OFF switch. When it's ON, current flows, and when it's OFF, the current stops flowing, which shows that the signal is changing. Therefore, it is important to wire it so that the direction of the current flow is correct.
An open collector output cannot output voltage on its own, so an external power supply is required to supply current. There are two types of open collector outputs, but Ono Sokki uses the NPN transistor type (sink type). It is necessary to wire it so that current flows into the collector terminal. The PLC receives an ON signal when current flows.
The diagram below shows a reference example of the receiving end of a PLC.
For actual connections, please wire according to the instructions provided with the encoder and PLC.
The basic principle is to consider the direction and path of the electric current when wiring.
This is a power source for supplying current, and you can also use the power supplied by a PLC (Power Line Communication).
Example 1:
Example 2:
Example 3: Using the PLC's internal power supply
reference:
Photocoupler:
This device combines a light-emitting diode (LED), which emits light when current flows through it, with a phototransistor, which conducts electricity when exposed to light. Because it acts as a light-activated switch, it provides electrical isolation between input and output.
Diode bridge:
It is also used as a circuit to take the absolute value of an AC signal that changes between ±.
Regardless of the direction of the input current, the output direction will always be unidirectional.
(Excerpt from the email newsletter issued on June 18, 2019)
