Calculate Encoder Resolution, Encoder Connect To PLC – PART 2


In the previous post, 365EVN show you the basic steps to select an encoder. Today, we will show you about: Calculate Encoder Resolution and Encoder Connect To PLC.

You can refer to the previous post before reading this post: select an encoder.

Calculate Encoder Resolution

Before calculating encoder resolution, we need some parameters:
  • The maximum speed of the system using encoder, unit: RPM (Revolutions Per Minute). We called this parameter is “A”.

For example, we use an encoder to calculate motor speed (the motor speed control by an inverter) and we direct connect it with the motor (4P, 380VAC, 50Hz). In this case, the maximum speed using to calculate the resolution of the encoder is 1500rpm (equal to maximum motor speed).

  • The maximum input frequency of Hight Speed Counter equipment (PLC, PIC…), unit: kHz. We can find it in the catalogue or user manual of Hight Speed Counter (HSC) equipment. And we called this parameter is “B”.

For example, with Siemens S7-200 PLC the maximum input frequency of HSC is 30 kHz (200 kHz with CPU 224 XP)

HSC s7 200

Could be helpful for you:

How to Calculate Encoder Resolution?

The formula for calculating the resolution of the encoder (Maximum) is: 

Max. encoder resolution (PPR) = (B*1000*60)/A

With the above example, we will select an encoder to calculate the motor speed with the maximum resolution is:

Max. encoder resolution (PPR) = (30*1000*60)/1500 = 1200 (PPR)

If we use CPU 224 XP the value is: (200*1000*60)/1500 = 8000 (PPR)

Encoder Connect To PLC (or Another Hight Speed Counter equipment)

In normal, we will see the power supply, output phases on the encoder. You can refer to the encoder catalogue to read more information.
  • Power supply: (5VDC, 24VDC…)

For example Encoder Omron (on photo): Brown-wire connects to DC+ (24VDC, 12VDC…). Blue-wire connects to DC- (0 V). And ground the shield wire to the frame ground (F.G) terminal.
  • đo tốc độ động cơ sử dụng encoderOutput phases (A, B, Z)

In normal we will use phase A, phase B connect to the input of PLC (or Another Hight Speed Counter equipment).

We need to read the catalogue to make an encoder connect to PLC.

For example, we use an Omron encoder (on photo) and Siemens S7-200 PLC. We use HSC2 Mode 9 for HSC function, and then we will connect Black-wire and White-wire to PLC inputs (I1.2 and I1.3)
  • With the PLC you can change the counter direction by changing the PLC inputs for phase A and phase B. In future, we will guide you to connect an encoder with some PLCs as Siemens PLC S7-1200, S7-200 SMART, Delta PLC…
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