Encoder Installation: Connecting Absolute Encoders to PLCs

As we know, absolute encoder encoder is a kind of rotary measurement device, it will be measured by the angular displacement directly into a digital signal. Therefore, we will input the output pulse signal of the rotary encoder directly to the PLC in the application, and use the high-speed counter of the PLC to count the pulse signal in order to obtain the measurement result.

It is important to note that the number of phases of the output pulses varies from one model of rotary encoder to another! Some rotary encoders output A, B, Z three-phase pulses, some have only two phases, A and B, and the simplest has only A phase.Encoder InstallationHigh-speed end mounting can fully utilize the full range and improve the resolution. The pull cord displacement sensor is a delicate composition of linear displacement sensor in structure, fully combining the advantages of angle sensor and linear displacement sensor, becoming a sensor with small installation size, compact structure, large measuring stroke and high accuracy, with a stroke ranging from several hundred millimeters to more than ten meters.

In this application, we connect a rotary encoder that outputs two-phase pulses to an FX-series PLC. So, how to connect it?

Normally, the encoder has four leads, two of which are pulse output lines, one is COM terminal line, and one is power line.

Rotary encoder and PLC connection method and rotary encoder selection attention to the place

The power supply of the encoder (the device that provides power to the electronic equipment) can be an external power supply or directly use (use) the DC24V power supply of the PLC. The power supply ;- ;terminal is to be connected to the COM terminal of the encoder and to the power supply terminal of the encoder. The COM terminal of the encoder is connected to the input COM terminal of the PLC, and the A and B two-phase pulse output lines are connected directly to the input terminal of the PLC.

Attention during connection: When connecting, you need to pay attention to the response time of the PLC input; some rotary encoders also have a shielded wire, when using the shielded wire should be grounded.

If the encoder is a parallel output, it can be directly connected to the input and output contacts I/O of PLC or host computer, and its signal math format should be Gray code. How many bits of the encoder should occupy how many bits of the PLC contact, if it is a 24-volt push-pull output, the high level is valid for 1, the low level is 0; if it is an open collector NPN output, the connected contact must also be NPN type, its high level is valid, and the low level is 1.

As a result, rotary encoder selection requires special attention to the following three aspects:

Mechanical installation dimensions, including positioning stops, shaft diameter, mounting holes; cable outlet method; installation space volume; working environment protection level to meet the requirements.

Second, the resolution, that is, the number of pulses per turn output when the encoder works, whether to meet the design and use of precision (accuracy) requirements. The output frequency of the encoder should not exceed the allowable range of the PLC.

Third, the electrical interface, encoder output methods are common push-pull output, voltage output, open collector, long line driver output. Binary encoder binary encoding is a pre-specified method of text, numbers or other objects coded into binary digital, or information, data converted into the specified binary electrical pulse signal. Its output method should match the PLC interface circuit.