Encoder signal output and transmission distance problem

Transmission distance of encoder

In theory, the maximum transmission distance of SSI is up to 400 meters (some technologies are needed to achieve this and enter our GP1312 instrument), and the maximum distance we apply to the Jiangsu Huai River into the sea is 300 meters.

The 16-bit parallel output can actually achieve a resolution of more than one-third of 30,000. The output is reduced on the main total range, and 4096 turns will not be used in most cases. Accuracy, such as elevation detection, such as sluice or hoisting lift, can reach the millimeter level. In fact, higher accuracy is limited by mechanical installation accuracy and it is meaningless.

For longer-distance transmission, the bus type can be used. I currently have encoder bus output types such as profibus DP, DeviceNet, Can, Interbus, etc., using meters or RS485 output types. Modbus is not recommended-slower.

The signal output principle of the encoder

The signal output has sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), push-pull multiple forms, of which TTL is a long-line differential drive (symmetrical A, A-; B, B -;Z,Z-), HTL is also called push-pull and push-pull output. The signal receiving device interface of the encoder should correspond to the encoder.

Signal connection—The pulse signal of the encoder is generally connected to the counter, PLC, computer, and the modules connected between the PLC and the computer are divided into low-speed modules and high-speed modules, and the switching frequency is low or high.

Such as single-phase connection, used for single-direction counting and single-direction speed measurement.

A.B two-phase connection, used for forward and reverse counting, judgment of forward and reverse and speed measurement.

A, B, Z three-phase connection, used for position measurement with reference position correction.

A, A-, B, B-, Z, Z- connections, due to the connection with symmetrical negative signals, the electromagnetic field contributed by the current to the cable is 0, the attenuation is the smallest, the anti-interference is the best, and it can be transmitted over a longer distance. For TTL encoders with symmetrical negative signal output, the signal transmission distance can reach 150 meters.

For HTL encoders with symmetrical negative signal output, the signal transmission distance can reach 300 meters.

Encoder selection precautions

Encoder selection should pay attention to the following three parameters:

1. Mechanical installation size: including positioning stop, shaft diameter, installation hole position; cable outlet method; installation space volume; whether the working environment protection level meets the requirements.

2. Resolution: It means the number of pulses output per revolution when the encoder is working, whether it meets the design and use accuracy requirements.

3. Electrical interface: Common encoder output methods include push-pull output (F type HTL format), voltage output (E), open collector (C, common C is NPN type tube output, C2 is PNP type tube output), long-line driver Output. Its output mode should match the interface circuit of its control system.