Determine Phase: A perfect Encoder should have a pulse output pattern like the one shown to the left.
When Channel A is on, Channel B should be on 50% of the time and off 50% of the time.
Count pulses: Pulses Per Revolution can be measured quickly. When the reference signal is received
the pulse counter starts then stops when the reference signal is received again.
This is useful when troubleshooting intermittent problems and damaged disks.
Can also be used on encoders with no reference signal.
Measure Voltage: When Channel A changes state, the meter measures the voltage of the Channel B pulse.
When reading a reference signal the voltage measurement is taken after a set period of time has
elapsed since the signal changed state.
Pulses can be 4......5000 pcs/360 degr.
This must be done with oscilloscope or best with special tester
from
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Encorer output types:
Differential Line Driver Output
A differential output refers to the fact that each channel has a complement channel,
i.e. Channel A and Channel A not. A differential line driver is used to help increase noise immunity.
A differential line driver also allows you to sink or source more current then a Totem Pole output.
A differential line driver will work both with a sinking or sourcing circuit. It can also help in
increasing the distance in which a signal is transmitted.
Push Pull Output
A Push Pull output is an output that allows you to connect either a sinking or sourcing circuit.
This type of an output allows you to sink more current than a Totem Pole output and follow the input voltage.
A Push Pull output is chosen when an Open Collector output will not work with the controller that is
connected to the encoder
Totem Pole Output
A Totem Pole output is essentially the same as a Push Pull output; however, it is the terminology
commonly used when referring to a TTL device. The major difference between it and a Push Pull is
the amount of current that it can sink or source. The Totem Pole output is going to sink/source less
current then a Push Pull output is capable of sinking or sourcing. The other major difference is the output voltage between the two. The Totem Pole is a 5V DC signal only, where the Push Pull will follow the input voltage.
Open Collector Output
An Open Collector output is a NPN transistor. A NPN transistor allows the sinking of current to common.
It can be thought of as a switch that allows the circuit, after the load, to be connected to common.
This means that a source is required for the output to work. A supply through a load must be connected
to the output, otherwise the NPN transistor is simply creating a path to common, i.e. a dry contact.
Therefore, if you were to measure the voltage at the output of an open collector that is not hooked up
to some supply you would not see a change in voltage. The voltage should be measured across the output
load to determine if the open collector is working properly.
Quadrature output
Quadrature output refers to the fact that the signals A and B are separated by 90 degrees of phase shift
with A leading B or B leading A depending on the direction of rotation. It does not mean that the output
will be 4 times the amount of the Pulses Per Revolution of the encoder. The fact that the signals are 90
degrees out of phase enables the controller to determine the direction that the encoder is spinning.
You must use both the A and B signal to have a quadrature output and to get X2 or X4 logic
From rsdoran May 2nd, 2002, 08:03 AM
PLCS.net Interactive PLC Talk Forum
Other output signal types:
Sine wave encoder
A variation on the Incremental encoder is the Sinewave Encoder.
Instead of producing two quadrature square waves, the outputs are quadrature sine waves
(a Sine and a Cosine). By performing the arctangent function, arbitrary levels of resolution can be achieved.
Absolute encoders
Traditional absolute encoders have multiple code rings with various binary weightings which
provide a data word representing the absolute position of the encoder within one revolution.
This type of encoder is often referred to as a parallel absolute encoder. (Serial data communication types found too)
The distinguishing feature of the absolute encoder is that it reports the absolute position of
the encoder to the electronics immediately upon power-up with no need for indexing.
Tachometer signal can be ac- or dc-voltage. Voltage must increase when rpm increases.
Signal must be proportional to rpm. (Measure voktage / rpm )
Tachometer signal can be also pulse train from magnetic sensor or encoder.
(Check as encoder)