There are many instances where Phidgets might get stuck outdoors: weather stations, RC vehicles (quadcopters, underwater vehicles, robots, etc), outdoor installations, and applications we haven’t imagined yet. Some specific examples of Phidgets in the outdoors are a giant drum machine, a sky temperature scanner and precision agricultural monitors.
In this series, we explore how to protect Phidgets from outdoor conditions, like rain and dust. In this post, we’re going to look at Phidgets that detect light, especially those in the infrared spectrum. Special materials are required to allow infrared light to pass through the casing, and each Phidget uses a different wavelength that require different materials, which we’ll discuss here.
Encasing Infrared Phidgets
For infrared Phidgets, on top of putting them inside of a weatherproof enclosure, as discussed previously, you’ll need to install a window in the casing, which the sensor can see through. Different kinds of sensors will require different materials for the window.
The easiest sensors to find a screen for is the 1143 Light Sensor 70000 lux (intended for outdoor light, unlike the 1142). This Phidget detects visible light (up to a wavelength of 560nm), so can use any standard glass lens. A single, un-distorted, flat pane with an anti-reflective coating gives the best results.
The 1045 Phidget Temperature Sensor IR uses long wavelength infrared (5.5 to 14 µm). Technically, a germanium filter should work, but in our tests with a germanium ND40k (optical natural density) filter, we had no success whatsoever. The fresnel filter seemed to pick up some readings, but the sensor needs calibration if you want accurate readings, and this will depend on the kind of fresnel filter you are using. The best way to use the Phidget IR temperature sensor is to have it pointing down and placed under a small tent to protect it from rain, or to only use the sensor outdoors when needed, then take it back inside when finished taking measurements.
The 1111 Motion Sensor works with a fresnel filter, but doesn’t offer quite the same range of values as when the sensor is fully exposed. Keep in mind that the sensor has a horizontal detection range of 38˚ and a vertical detection range of 22˚, which will change when the sensor is enclosed. If you’re using the motion sensor more or less as a switch, then the fresnel filter won’t pose any problems for your project. The 1102 and 1103 Distance Sensors (5mm and 10cm, respectively), worked best with the fresnel filter. Much like the motion sensor, they’re best used as a switch for detecting nearby objects. The filter does not change any of the readings.
For the Sharp Distance Sensors (3520 4-30cm, 3521 10-80cm, and 3522 21-150cm) there are a few options. These sensors emit light with a wavelength of about 950nm, in the near-infrared spectrum. We used a 950nm infrared optical grade filter. When using this filter in front of the 3520 and 3521, the sensors returned accurate results without needing any calibration. Fresnel filters also worked on these two sensors, but they need recalibration. Non-reflective glass is the only medium that works for all three Sharp distance sensors, although recalibration is still needed.
For quick reference, here are the kinds of filters that work for the different Phidgets IR sensors:
Installing the Lens
Now that you know what filter to use, you’ll still need to install it in an adequately weatherproof case. With these sorts of filters, it’s very unlikely you’ll be able to get more protection than IP64.
- Choose a lens that’s the right size for your sensor and an enclosure that will fit the rest of the hardware and provide you with the adequate amount of weatherproofing. I chose a 30mm lens, which fit the distance sensor very snugly. If I do this again, I’ll use a larger lens. It won’t hurt anything.
For the case, I went with the BUD Industries PN-11327, which gave a good amount of space to work in.
- Drill a hole in the enclosure, so that the lens will fit very snugly. Apply a bead of silicone around the perimeter of the hole and fit the lens in. Follow the directions provided with the silicone to make sure the seal sets properly.
- I used a piece of plexiglass to mount the hardware, but other materials, like wood or metal, work equally well. Once the plexiglass is cut to fit the container, drill holes to (a) mount the plexiglass in the case and (b) mount the hardware on the plexiglass. Be careful to line everything up properly. I drilled the holes for mounting in the case first. I then installed the piece of plexiglass and figured out where the other holes would need to be drilled. Make sure to take into account where the wires are going to be running.
- Install the sensors using the mounting hardware that comes with Phidgets: 4 nuts and bolts (M3 x 18mm), 4 plastic spacers. Be sure to use spacers and try to minimize the gap between the sensor and the lens.
- Now’s a good time to install the connector onto the case. Once you’ve chosen what kind of connector you are going to use, drill a hole for it and connect it up. Depending on the approach you’ve chosen, this could involve some soldering. Make sure that if you’re using cable glands or circular connectors that you put them onto the cables before soldering any other connections (I’ve made this mistake more than twice). I used a USB connector that the interface kit will connect to.
- Put the plexiglass mount in the case and screw it in. Connect your cables. Seal up the box.
Now all you have to do is mount the box where you want it, and you’re ready to go. The same installation technique can be applied to any type of lens, sensor and connector combination you choose for your project. Now, you know how to use any of the Phidgets infrared sensors in the outdoors.
If you missed it, check out other posts in this series, like which enclosures and connectors to use or how to control the temperature of outdoor Phidgets. Next week, we’ll look at the last group of Phidgets for this series, those that cannot be weatherproofed.