Measurement Specialties USB-1616HS-2 manual Maximizing encoder accuracy

USB-1616HS-2 User's Guide Functional Details

Maximizing encoder accuracy

If there are 512 pulses on A, then the encoder position is accurate to within 360°/512.

You can get even greater accuracy by counting not only rising edges on A but also falling edges on A, giving position accuracy to 360 degrees/1024.

You get maximum accuracy counting rising and falling edges on A and on B (since B also has 512 pulses.) This gives a position accuracy of 360°/2048. These different modes are known as X1, X2, and X4.

Connecting the USB-1616HS-2 to an encoder

You can use up to two encoders with each USB-1616HS-2 in your acquisition system. Each A and B signal can be made as a single-ended connection with respect to common ground.

Differential applications are not supported.

For single-ended applications:

ƒConnect signals A, B, and Z to the counter inputs on the USB-1616HS-2.

ƒConnect each encoder ground to GND.

You can also connect external pull-up resistors to the USB-1616HS-2 counter input terminal blocks by placing a pull-up resistor between any input channel and the encoder power supply. Choose a pull-up resistor value based on the encoder's output drive capability and the input impedance of the USB-1616HS-2. Lower values of pull-up resistors cause less distortion, but also cause the encoder's output driver to pull down with more current.

Wiring to one encoder: Figure 21 shows the connections for one encoder to a USB-1616HS-2 module.

To external power

Ground (to Digital Common1)To ground2

Counter 0 (CNT0) – To Encoder “A”

Counter 1 (CNT1) – To Encoder “B”

Counter 2 (CNT2) – To Encoder “Z”

1The ground depicted at the left is associated with Digital Common on the USB-1616HS-4.

2The ground depicted at the right is associated with the external power source.

Figure 21. Connections from single encoder to screw terminals on the USB-1616HS-2

The "A" signal must be connected to an even-numbered channel and the associated "B" signal must be connected to the next higher odd-numbered channel. For example, if "A" were connected to counter 0, then "B" would be connected to counter 1.

Connect each signal (A, B, Z) as a single-ended connection with respect to the common ground. The encoder needs power from an external power output (typically +5 VDC). Connect the encoder's power input to the power source and connect the return to the digital common of that source.

Wiring for two encoders: The following figure illustrates single-ended connections for two encoders. Differential connections are not applicable.

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