Would SEN recommend Conformal Coating External Sensor Boards?
Conformal Coating External Sensor Boards – Would SEN recommend conformal coating sensor boards that are going to be used in moist external environments?
A: It depends. We’d probably start by purchasing sensors with IP67 or IP66 ratings if we were going into install sensors in fully exposed locations.
There aren’t many of these, so finding something will require a search and a preparedness to pay for the best quality. You want your sensors to have sunshades, as well as appropriate seals. Sensors with IP55 ratings can survive outside if they have a little protection.
Whether or not you undertake a conformal coating of sensor boards is up to you – you’ll need to check with the manufacturer to ensure this does not breach warranty – the boards may already be coated and might not need an additional layer.
Cheerily spraying coatings onto boards is asking for trouble. You’ll need to mask the connectors, switches and sockets – failing to do so may impact on circuits. You can mask switches with a little gob of silicone that you pop out again after the conformal coat dries. Another way to handle this is to make sure all the connections are plugged in while you are spraying.
Polyurethane sprays like Humiseal UV550 are ideal. When applying the spray be careful not to apply heavy coats that might sneak past masking and onto terminal screws, programming plug-in contacts, battery connections or tamper switches and between light coats be sure to let the board sit for 5 minutes.
Something else to think about with intrusion detectors is spraying anything onto boards which have unmasked PIR sensors on them. Conformal coatings are electrically insulating, so spraying a film over a piezoelectric sensor is going to blind the device. You’ll need to carefully walk test to ensure normal operation.
In SEN’s opinion, the best way to protect external sensors is to keep them away from direct sunlight and weather by protecting them with integrated sunshades, locating them under eaves or whatever cover you can find, including by customising simple protective cover that can be positioned above them.
If possible, ensure the lens of an externally mounted sensor is never exposed to direct sunlight. If it is, add replacing the lens into maintenance schedules. You need to be on top of external cabling requirements in any environment impacted on by moisture, salt and sun – entry cables are a particular concern. At times a unitised wireless sensor might be a better choice.
There will also be vibration, impact, thermal expansion and contraction, UV damage, damage from chemicals, etc, to contend with. Try to buy hardware that was built to handle such conditions – the last thing you want is unstable poly falling apart 18 months in.
You can check the integrity of the conformal coating using a blacklight (UV light) and touch up bare patches with the spare Airfix brush you’ve been saving since you built that Messerschmidt BF109 in first form. An alternative to using an external sensor is to use the movement detection functions of an IP67 CCTV camera to drive an alarm input.
More datails about Conformal Coating External Sensor Boards from HumiSeal here and read more SEN news here.
“Would SEN recommend Conformal Coating External Sensor Boards?”
