Add Safety and Accessibility With Remote Amplifiers

Why did the sensor cross the road?

To work remotely, of course.

Even sensors are working remotely these days, and some have good reason. Many applications dictate that the sensing element be placed remotely from its associated electronics. Let’s looks at a few common examples of this.

This may be for safety’s sake, such as in oil and gas applications where housing the bulk of the electronics away from a hazardous area reduces the likelihood of an electrical discharge, or where there are environmental concerns, such as temperature or vibration. By placing the majority of the electronics safely away, only the minimal number of components are subjected to the extremes.

Another good reason for remote placement is accessibility. In some cases, for example, the sensor must be mounted in a difficult to reach place, and having remote electronics installed in a more accessible location allows for easier access for the needed periodic re-teaching, adjusting, etc.

Separate electronics are also used when the sensing element needs to be designed into a very tight space. These very small sensor elements are likely to be customized to fit into a device directly, often leaving no room for the remainder of the electronics.

Remote placement is typically used out of necessity, but it doesn’t have to limit sensor capability or performance.

A typical amplifier with jog button, selector switch, and display.
Typical amplifier with jog button, selector switch, and display

Separately housed electronics, known as amplifiers, can do more than just house the electronics that support the sensing elements; they also provide a way to configure the sensors through buttons and displays. The amplifier delivers the smart features that larger sensors possess, without increasing the sensor size.

Let’s take a look at an amplifier designed to work with the micromote photoelectric sensors.

Micromote photoelectric sensor with 2mm diameter.
Micromote photoelectric sensor with 2mm diameter

Micromotes are extremely small photoelectric sensors that direct a very tight beam of collimated light at a target. The light emission is specifically engineered for the application, either attenuating or refracting as it interacts with the object to be detected. Many of these applications involve detecting very small bubbles in a stream of fluid, micro-bubbles that are smaller than the human eye can detect.  Others may be used to detect the edge of a microscope slide or count very small drops of liquid.  They are precision engineered to detect small objects in small spaces.

The amplifier will receive a power source, and in return it will provide power to the sensing element. But beyond the supporting electronics, what else might a good amp do?

    • Provide a choice of output types (PNP/NPN/Analog/NO/NC)
    • Supply an adequate frequency response for the fast counting of objects
    • Use LED indicators to help troubleshoot connections and warn of unstable signals
    • Provide on/off signal delays (pulse stretching) for those super fast applications
    • Allow the signal hysteresis to be adjusted to suit the application
    • Provide a way to lock the set parameters from inadvertent changes
    • Offer an alarm output if the application is out of specified limits
    • Include a display to navigate through the menus and to display signal strength when operating
    • Teach the application through the use of selector switches
    • Deliver auto synchronization

So, the next time you have a demanding application that requires a sensor to work remotely, consider a premium amplifier — one that not only supports the sensing element, but provides the smart features that today’s best sensors offer. You just might find that working remotely has many advantages, including a more integrated final product, which is more accessible to tune, and with additional features.

Detecting Small Bubbles? Consider These Factors First

BubbleDetectionBubble or air-in-line detection is a common lab automation application. In these types of applications it’s important to know whether or not liquid is flowing through a line to ensure safe and proper function in liquid-handling processes.  As these processes utilize smaller and smaller volumes of liquid — which provides cost and time saving benefits — it becomes more and more difficult to detect the potential air pockets forming inside the line. The most common approach in detecting these minute air pockets is a through-beam, photoelectric bubble sensor.

Photoelectric bubble sensors provide non-invasive detection of fluids and air pockets residing inside a tube. They have fixed opening dimensions for standard tube sizes allowing the selected tube to sit in perfect position between the sensor’s optical components. When the sensor’s light beam is blocked by fluid (or an air pocket) inside the tube, the received signal varies and external electronics determine if the signal variation is above or below the set threshold. Once the threshold is met the sensor’s output is switched.

Detecting bubbles sounds quite straightforward and simple, but in reality the application can be somewhat complicated. Several factors should be considered for reliable detection. Listed below are a few factors to consider:

  1. Tube diameters (inner and outer)
  2. Tube transparency
  3. Liquid type(s)
  4. Liquid transparency

Tube Diameters

Tube Sensor DrawingBecause a tube acts as a lens for light to travel it’s important to factor in the tube diameters. If there is a large difference between the outer and inner diameters of a particular tube, the outcome is a relatively large tube wall. A large tube wall will allow light rays to travel from the emitter through the wall straight to the detector without passing through the inner diameter of the tube, where the liquid or bubble is present. This causes unreliable detection. By accounting for both the inner and outer tube diameters a proper determination can be made in selecting what type of sensor to use to ensure that light only passes through the inner diameter of the tube and not through the wall.

Tube Transparency

Since photoelectric tube sensors operate on the principle of light detection, light must make it through one end of the tube and out the other end. Therefore, the transparency of the tube is critical. If the tube is opaque a photoelectric sensor solution is unlikely; however, in some cases it’s possible for a photoelectric tube sensor to detect through an opaque tube.

Liquid Type(s) and Transparency

The liquid type(s) and transparency are critical when determining which photoelectric tube sensor to use. If the liquid type is non-aqueous, without factoring in its transparency, it’s best to use the principle of light refraction through the liquid. If the liquid type is aqueous and is completely transparent or semitransparent, it’s best to use the principle of light absorption through the liquid. The following table will help determine what type of sensor to use with respect to the liquid type present inside the tube.


Since the type of applications that require precise bubble detection range in specifications from the use of hundreds of different liquids to specialized tube dimensions, this post only touches the surface of the photoelectric sensors for bubble detection.  For more information on tube sensors, please visit the Balluff website.