Panel Encoders

Optical manual encoders belong to the incremental encoders (see the guide). However, they are also mainly used as setpoint devices by hand. In this case, setpoints are output as electrical signals in the form of increments by means of a manual rotary movement of the encoder axis (clockwise or counterclockwise). Our portfolio includes only encoders with optoelectronic sensor principle. They may have additional features such as integrated push buttons and/or so-called detents. If a push-button is integrated, a switching contact is closed when axial force is exerted on the shaft. With the detent option, the torque changes in equidistant steps when the shaft is actuated.

Popular applications are:

• Changing the volume, for example in AV receivers, CAR audio systems
• Scrolling through menus
• Specification of numerical values
• Confirmation of a function or setpoints

Optical incremental encoders supply their useful signal in the form of pulses. To detect the direction of rotation, the encoders provide two electrical signals at the output, those of channels A and B, whose signals are phase-shifted by 90°. An evaluation unit uses the relationship of signals A and B to detect whether the axis of the encoder is rotated clockwise or counterclockwise. The optical sensor technologies have several advantages. It is a contactless measuring principle, i.e. the measured value transmission between the measured value recording and the measured value acquisition takes place without contact. For more details on optical incremental encoders, see their guide.

Encoders with detents provide the operator with haptic feedback. This feedback is expressed by a noticeable periodic change in mechanical resistance during rotation. Detents are only available as an option for these encoders. In most cases, the number of detent positions and the detent torque can be selected. More precisely, detent means the change in operating torque in equidistant steps during rotation of the shaft. The shaft always detents between two positions and only by applying an increased force can the position be changed. The detent position is called "Detent Position". Electrically, a change of state of the signal output levels occurs between two successive detent positions or during the change of the detent position. An evaluation unit is used for this purpose.

The pulses can be used for example for the following applications:

• Generally for increasing or decreasing a numerical value per detent position
• For navigation in a menu structure by means of a rotary motion - any detent position corresponds to a change of the menu position

The force used to overcome the detent position is also called detent torque in data sheets. The higher the detent torque, the higher the force that must be applied to rotate the shaft of the encoder and thus change the setpoint while maintaining the diameter of the adjustment knob.

The purpose of an increased detent torque is

• To prevent unintentional rotation of the shaft and thus to counteract an unintentional change in the setpoint
• To compensate for the relationship between the adjusting knob diameter and detent torque. The larger the diameter of the adjusting knob, the longer the lever (r), which acts perpendicular to the centre axis of the shaft, and the less force (F) is required to turn the adjusting knob and thus the axis of the encoder at the same detent torque.

Many encoders have an integrated Schmitt trigger. The Schmitt trigger is an electronic circuit. The data sheet of each encoder contains a (block) diagram of the encoder electronics. From this diagram it can be seen whether the encoder has an integrated Schmitt trigger.

With this circuit a change of state of the output signal between two fixed level states low/high and vice versa is realized. For this purpose, signal amplitudes at the signal input of the Schmitt trigger must change within a certain range, the so-called "treshold level". The general rule is

• a Schmitt trigger always outputs square-wave signals
• if the frequency of the input signal changes, then the frequency of the output signal also changes
• the waveforms of the input signals at the Schmitt trigger can be different. For a level change to occur at the signal output of the Schmitt trigger, the signal amplitude of the input signal must change in the range of the switching thresholds

Encoders are very often used as manual adjusters. Therefore, they are optimized for manual operation of the shaft.
A higher operating torque is required for safe input of setpoints. This is the only way to set precise setpoints and to counteract unintentional rotation of the shaft.
The torque describes the rotational effect of a force which must act on the shaft in order to rotate it. The unit for the torque is Newton metre [Nm]. In order to increase the torque, rotary encoders with plain bearings are used, and the anti-rotation is achieved by means of a damping grease and/or spring element to generate additional friction. The use of a ball bearing makes no sense due to the low (breakaway) torque.
The torque must be specified taking into account the operating temperature and the number of shaft movements. The lower the operating temperature, the higher the operating torque. A longer standstill of the shaft and the confirmation speed (rpm) also have an influence. Often the torque is specified in a data sheet at room temperature and an actuating speed with constant 10 rpm.
For technical reasons it is not possible to represent the specification by means of a single value. This is only possible for one value range. Reasons for this are mainly tolerances of the shaft bearing and shaft as well as the quantity and positioning of the damping grease on the shaft and shaft bearing. Typical information about an operating torque in data sheets is
0.1 ≤ M ≤ 0.6 Ncm / 0.3 ≤ M ≤ 1.3 Ncm (@RT, 10 rpm)
The abbreviation RT stands for the reference of the torque measurement to the room temperature and is located between 19 °C and 21 °C according to the standard for residential and office buildings.

In addition to the characteristics such as operating torque or detent torque, the rotary knob plays a decisive role in the haptic properties of a rotary encoder. Mass and outer diameter are the most important factors here.
Handwheels usually have a setting head with a high mass. If a fast rotary movement is performed and the setting head is released, the relatively high mass of the setting knob prevents the encoder shaft from stopping abruptly. This means: The increased mass of the rotary knob leads to a briefly continuing rotary motion of the shaft (overshoot characteristic due to mass inertia). This can be advantageous for setpoints that need to be changed quickly, because this effect supports the rotation.
With rotary encoders from MEGATRON in the handwheel version, a crank handle is also integrated in the rotary knob. In the case of handwheels, the rotary knob is part of the scope of delivery and is already attached to the rotary encoder. For all other rotary encoders, a rotary knob must be selected as a further accessory.