Multiple Sensing Modes for Miniature Capacitive Sensors

MiniCapacitiveIn a previous blog post we discussed miniature capacitive sensors and their use for precision and small-part sensing. Here we will discuss the different sensing modes available with separately amplified miniature capacitive sensors.

Standard Switching Mode


This is the most commonly used teach method for most sensing applications. As an object is placed statically in front of the sensor at its desired detection point, the amplifier is triggered to teach-in this value as its switch point (SP1). Once the value is taught, the output will then switch when the switch point is reached.

Two-Point Switching Mode


As the name sug
gests this teach method has two separate teach-in points, a switch-on point (SP1) and a switch-off point (SP2). These points can be taught wide apart or close together, depending on the application need. One application example is for fill-level control by teaching in min. and max. fill-level points.

Window Function Mode


This teach method creates a window between two separate switch points (SP1 and SP2). If the sensor value falls inside this window, the output will switch on. If the sensor value is outside of this window, the output remains off. An application example is material thickness (or multiple layer) detection. If the material is too thin or too thick (i.e., sensor value is outside the window) the output remains off; however, if the material is at the correct thickness (i.e., sensor value falls inside the window) the output switches on.

Dynamic Operation Mode

This mode only responds to moving objects and ignores static conditions. This mode is commonly used to ignore a close background, and only detect objects moving in front of the sensor.

Analog Output Mode

Additionally, an analog output (either voltage or current) is available. To utilize the whole analog range, two separate teach points are needed. SAHi, analog signal high, and SALo, analog signal low, are taught accordingly to obtain the full range. An application example would be continuous fill-level detection across the sensing area.

For more information on capacitive sensors and their remote amplifiers, click h

Photoelectric Basics – Light On or Dark On

Recently I was asked if light on and dark on for a photoelectric sensor was the same as normally open and normally closed.  The short answer is yes, but I think it justifies more of an explanation.  In the world of proximity sensors, capacitive sensors, and mechanical switches when the target is present the output changes state and turns on or turns off; there is no ambiguity.

With photoelectric sensors, instead of normally open or normally closed we refer to light-on operate or dark-on operate because we are referring to the presence or absence of light at the sensor’s receiver.  The output of a light-on operate sensor is on (enabled, high, true) when there is sufficient light on the receiver of the sensor.  Conversely, the output of a dark-on operate sensor is on when the light source is blocked or no light can reach the receiver.

There are three modes of operation with photoelectrics: diffuse, retro-reflective, and through-beam; and the sensing mode determines if the sensor is normally light-on or dark-on.  Retro-reflective and through-beam sensors function as light-on operate sensors because under normal operating conditions there is a reflector or a light emitter providing a light beam back to the sensor receiver.  If no object is blocking the light beam to receiver the output is on, normally closed.  If the target or object is in between the reflector or emitter then the light beam can no longer reach the receiver causing the output to turn off.

Since the diffuse mode of operation requires the target or object to reflect the light source back to the receiver, it functions as a dark-on operate, normally open.  If no object or target is placed in front of the sensor, no light will be reflected back to the receiver.  When the object is present, the output changes state from normally open to closed.

The chart below should help to summarize the above: