Control.com - Nerds in Control

Dear all participants,

i'd like to ask you about the rotary encoder.

once i've read that there are 2 different incremental encoder,they are 5V and 24 V encoder. Is it means the encoder supply? or it is the maximum Amplitude level of encoder's output Pulse??

my next question is, How about the encoder with 6 output signals (encoder with inverting A, B, and N signals instead of A, B and N)?

what are the function of inverting A, B and N? can i use only the A, B and N signal to measure the speed and knowing the rotation direction??

all i know the encoder only have 3 output. "A" for speed, "B" for rotation direction, and "N" for setting the counter default.
Is this correct??

please revise me if I'm wrong, i would also thank if you don't mind to share the knowledge on it.

My best regards,
Irwan

> 5V and 24 V encoder. Is it means the encoder supply? or it is the maximum Amplitude level of encoder's output Pulse?? <

It means the voltage of the output signals.

> what are the function of inverting A, B and N? <

Because sometimes you need an inverted signal, especially if you are doing anything other than just counting the pulses. You might have an input device that needs a falling edge instead of a leading edge, and you want it to trigger at a specific angle.

> can i use only the A, B and N signal to measure the speed and knowing the rotation direction?? <

Yes.

> all i know the encoder only have 3 output. "A" for speed, "B" for rotation direction, and "N" for setting the counter default. Is this correct?? <

No, it is not correct. It is possible to count only one phase, but most dedicated encoder counters use both. A and B are two phases of a "quadrature" signal. They are out of phase with each other, and the order in which they change can be used to determine the direction of rotation. If you draw two square waves which are 90 degrees out of phase with each other you will see how this works. Both signals though are usually used by an encoder counter for speed or distance as this effectively gives more pulses per revolution (4 times as many if you count both rising and falling edges).

The third signal ("N" in your case) is usually a one pulse per revolution signal marker pulse. This is typically used to help in getting a repeatable position for homing a linear axis. The signal is combined with an external homing switch, with the homing switch providing the absolute position, and the marker pulse providing a more accurate refinement of it.

I believe that the 24VDC is just the supply voltage, I have always used 5 VDC encoders. Outputs are typically 5 DCV. CMOS outputs are sometimes rated up to 15 VDC. If you get NPN transistor outputs, they will sink current up to a certain voltage limit.

The ABC alone can work fine, but adding the /ABC channels reduces common mode noise by using a differential signal. The noise that is present on both signals will be cancelled out.

The C channel is a once per rev index pulse, used for homing a motor with precision or resetting a counter every revolution. You may or may not need the C channel. The AB alone (or with /AB) channels will provide distance, velocity, and direction information.

Bill Sturm

Just to add what has been posted. The voltage rating means input and output. Many encoders are rated for a range of voltages, for example 5-24VDC. Most encoder inputs for motion controllers are rated at 5VDC.

On the 5V/24V thing. You have to pay attention to input AND output. Some encoders take 5V and output 5V. Some take 24V and output 5V. Some take 24V and output 24V. I've never seen a 5V in - 24V out, but I suppose it's theoretically possible. Most encoders take some range in and spit 5V out. 5V in - 5V out is the most common, but situations vary.

The reason for having A, B, and N as well as not A, not B, and not N is to increase immunity from noise. They are not strictly necessary. Again, it depends on your situation. Most encoder cards can take this "differential" signal, but some can't. Most encoders supply both because it's easy to have and doesn't hurt anything; you can always just not hook them up.

BTW, some people say A,B,N, some say A,B,C, and some say A,B,Z. I kinda prefer Z, myself, but it doesn't really matter.

"can i use only the A, B and N signal to measure the speed and knowing the rotation direction?"

Yes, and in fact you don't need N at all. Just A and B will tell you speed and direction. Well, it tells you PULSES and direction; you have to have some other means of determining time in order to calculate speed.

-James Ingraham
Sage Automation, Inc.