Encoder is used for measuring the relative position (displacement), displacement velocity and direction by means of optical angular or linear displacement sensors (encoders) connected to the ADC input channels.
Encoder generates virtual channels for displacement and displacement velocity. These channels are available for further analysis with other ZETLAB programs.
The Encoder indicator displays the measured angular or linear displacement (position) and displacement velocity. Based on the task, the displacement is measured in the specified units of measurement, and the velocity – in units of measurement per second.
The resolution of an incremental encoder is determined by the number of pulses per one revolution (pulses per revolution, ppr). The necessary number of markers per the set unit of measurement is selected in the program. For instance, an incremental angular displacement encoder has 1080 markers per one revolution, and 3 markers per one degree of turn respectively. It is necessary to measure the encoder position in degrees with a precision up to one degree.
To do so, one needs to select a unit of measurement in the program – degrees, and to set 3 in the box Resolution (three markers per one degree of encoder rotation).
It is possible to specify the upper and lower signal threshold levels in the Encoder program (manually or by switching to the automatic determination). The upper and lower limits are set exclusively for false activation in course of displacement measurements. It is possible to determine the maximum and minimum signal levels for the channel, to which the encoder is connected, e.g. by starting Multichannel Oscillograph, selecting this channel and evaluating these levels on the oscillogram.
The program also provides a graphic indicator which shows the integral signal level and encoder channel congestion, in case the maximum acceptable level is exceeded.
Encoder is to be used with channels which are output signals for linear and angular displacement sensors.
Linear and angular displacement sensors are based on optical sensors. The accuracy of such sensors can vary from 1 µm to 1 mm, if the measuring base is 8 mm to 3 m long. Angular displacement sensors can have 100 to 10,000 markers for one revolution, i.e. the resolution can vary from several degrees to 5 minutes.
Optical technology provides a number of classic ways for building an encoder – a sensor providing information about movement, position, or direction either directly in the digital form (absolute encoder) or by generating a pulse sequence (incremental encoders).
The Encoder description below is to deal with incremental encoders only, since the Encoder program is designed to operate such sensors. The functioning of incremental encoders is presented in the figure below. An optical encoder consists of a thin optical disk and a fixed block – measuring probe, including a light source and a photocell. The optical disk has a surface with transparent and non-transparent sections. The holes in the metallic sheet or marks on the glass disk can serve as markers. As the disk rotates, depending on its type, the markers conduct or block the light beam directed from the light source towards the photoelectric receiver.
The photocell generates a signal with a frequency equal to the code element repetition rate in the digital form, or an analogue pulse signal, which can also be reinforced and digitalized. By adding another LED-optical transistor pair with an angular displacement in relation with the first one, corresponding to one fourth of the signal period, another pulse sequence can be obtained – Channel B with a 90° phase displacement with reference to Channel A. An incremental encoder, using two optical channels, enables simultaneous duplication of the resolution by measurement of the position and velocity and determination of the direction. The third channel is used for referencing to the initial marker (0 marker).
To measure the displacement (position) and displacement velocity, it is necessary to set the parameters of the channel, to which the encoder is connected, in ZET Device Manager tab. The parameters of measuring channels are to be set with reference to the voltage measurement, as shown in the figure below (names of channels are specified by the user):
Sensors can be powered through the integrated generator output (if supplied with an integrated generator) by generation of a 5 V sinusoidal signal with constant zero displacement or by means of an external 5 V power supply:
The figure below shows the oscillograms of signals coming from the angular displacement sensor. The upper oscillogram shows the signal of the encoder’s Channel A (Phase A), the central oscillogram – Channel B (Phase B), the lower oscillogram – zero marker signal (0 marker):
Input data for Encoder includes digital data of the ZETLAB server channel.
Encoder is included into the following software packages:
Encoder is included in the Measurement software group:
