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Splat! Goes the Sensor by Britt Storkson Owner, P2FlowLLC Popular Mechanics magazine reported sensors used on self-driving cars can be defeated - meaning rendered inoperable and useless. What defeated these devices? Was it the work of devious hackers? Could mali- cious vandals be the culprit? These sensors were defeated by bugs - common, ordinary bugs that you clean off of your windshield from time to time from early spring to late fall when the bugs are active. Ford Motor Company developed an air “shield” which uses several streams of compressed air to divert the bugs away from the sensor. Similar systems use windshield washer fluid to periodically clean off the bugs. As is the case with most every- thing, changes in one area require changes in one or more other areas to ensure reliable operation as each of these solutions comes with their own set of problems. The air “shield” does not work 100% of the time, and what if the fan supplying the air quits? With a heavy bug load, the windshield washer fluid could be used up very quickly - rendering the sensor useless. Sensors are a critical part of automation. If one or more sensors are not working, or not working properly, unless there is some redundancy built in your system, it won’t be working for long. Sometimes compromised sensors do not quit sending information entirely. The information can be there, but so corrupted the controlling computer does not get the accurate infor- mation it needs to make the right decisions. What is a sensor? A sensor converts a physical stimulus into a voltage. This stimulus may be temperature, pressure, phys- ical position, and chemical - to name just a few of many types of sensors now available. What this output voltage represents is defined by the sensor manufacturer, and there are thousands of different sensors out there with a wide variety of output configurations. This output voltage is routed to a device called an analog-to-digital converter, which extracts a digital “word” the computer can use. Most sensors are “ratiometric”, meaning the output is directly proportional to the input. A simple example of this concept is a pressure sensor with a voltage output of 0-10 volts with a 0-100 psi full scale range. If you hook it up to a pressure source and read (with a voltmeter) 1 volt at the output, it means you have 10 psi at your pressure source; 2 volts would indicate 20 psi; 5 volts would indicate 50 psi; and so on. For critical systems, often two or more of the same sensor are used. If one sensor fails or transmits flawed data, the com- puter control can be programmed to ignore it and only accept data from the properly working sensor. A good control system will also advise the operator not only that a sensor has failed, but identify which sensor failed so it can be repaired or replaced. How do we determine we have a bad sensor? All sensor outputs operate with a maximum high and low voltage, and one way to determine if the sensor is working right is to check to see if the sensor output is within the correct voltage range. Another way to check for a bad sensor is to note if the sensor output does not change within a certain time frame. This would suggest the sensor is jammed in place or frozen. This is useful for something like an “angle of attack” sensor which determines the angle of the aircraft fuselage relative to the ground. But what if a critical sensor or multiple sensors do not work and the computer cannot compute? What do we do then? Currently, the conventional wisdom is to disconnect everything and hand the control back to operator, or shut off everything completely so the equipment doesn’t damage anything. But what if the operator isn’t paying attention or isn’t aware the control system isn’t controlling anything anymore? That’s when we should reconsider whether or not the equipment should be automat- ed to begin with - or automated on a lim- ited basis to aid the operator instead of replacing the operator entirely. Automation doesn’t automatically make everything better. Incompetent or incomplete automation can cause more problems than it solves; increase costs because you have to have an operator anyway even with the automation; and even create safety hazards that would not exist without it. Like most every technology, proper application is important - and automation is no exception. Britt Britt Storkson may be contacted via e-mail to michele@ worldwidedrillingresource.com 7 WorldWide Drilling Resource ® MARCH 2020