Video: McON AIR COMPACT – Operation

Video transcript

What is inside the box, how it is wired, and how to get a reading you can trust out of it. Three rules before anything else, and all 3 come from experience rather than from caution. Keep the principle in mind while you install it, because every rule that follows comes from it: two sensors, a fixed distance, and a delay to measure. And inside, the chain is short.

Each rod picks up a faint electrostatic signal. The box amplifies it, digitises both channels, and runs the cross correlation that finds the delay. From the delay it computes the velocity, and puts it on the current loop. Choose the spot with that in mind. The best place is the throat of a venturi, where the flow is fast and orderly. Failing that, a straight run with room before and after. If the gas is clean or slow, the range extender goes upstream of the sensors.

Its distance is set by the duct, not by convenience. The two sensors go in parallel, on the double support, and their cables point the right way: sensor one upstream, sensor two downstream. Getting that backwards gives you a negative velocity and a puzzled afternoon. The box itself asks for little, but that little matters: keep it reachable, keep it out of the weather, and keep it away from radiated heat. Everything plugs into the front edge.

Two fuses, the supply, the range extender, the serial port, the two sensors, the filter breakage option, the measured value output, and the reset button. Two plugs you terminate yourself. The supply: pin 1 is 24 volts, pin two is protective earth, pin 3 is ground. And the output plug carries the current loop on pins 1 and 3, with the fault contact on 2, 4 and 5. Terminating them is fiddly but exact. Strip 21 millimetres of sheath and 6 of insulation,

crimp a ferrule and cut it back to 5, and tighten each screw to its own torque. Once it is powered, the box talks to you through 4 indicators, and the colour code is the same for all of them: green is fine, yellow is not active, red is an error. What leaves the box is a 4 to 20 milliamp signal that you scale, plus a contact that tells the control system when the value cannot be trusted. And below 4 milliamps, the current itself is the error message. The box has no buttons, so everything is set from a laptop over the serial adapter.

Install the driver first, then the program, and work through it in this order. The scaling factor deserves a word of its own. It is how you reconcile what the system reads with what a reference instrument says at the same spot, and it is the only adjustment the system needs. In service it needs almost nothing: a look at the boxes, a look at the rods, and the occasional fuse. And when the reading misbehaves, work through it in this order before calling anyone.

Process measurement, from Amperis.