R.M. Young 05501LM Wind Monitor I.S.

Wind measurement inside a classified area is a problem of signals rather than of wind. The mechanical part of an anemometer is inert - a propeller and a vane - but the electrical part generates and carries signals, and in a Division 1 area, where a flammable atmosphere may be present under normal operation, that circuit has to be incapable of igniting it. The 05501LM is the intrinsically safe version of the Wind Monitor, and YOUNG state it can safely be used in Class 1, Division 1, Group A, B, C and D hazardous areas - which is the widest of the North American gas group classifications, Group A being acetylene and Group B hydrogen.

The sensing principle is the familiar one. A four-blade helicoid propeller measures wind speed, generating an AC sine wave as it rotates, and direction comes from a vane attached to a precision potentiometer inside an internal housing. That gives the same well-characterised response as the rest of the Wind Monitor family, which matters because a hazardous-area installation should not mean accepting a less capable instrument.

What differs is what happens to those signals. Internal circuitry converts them into isolated 4 to 20 mA current outputs, and the choice is significant in two ways. Intrinsic safety depends on limiting the energy in the circuit, and a current loop is straightforward to constrain and to certify with a barrier or isolator at the safe-area end. Beyond the certification, 4 to 20 mA is the right output for a long run in an electrically noisy industrial environment - current loops are immune to voltage drop over distance and reject induced noise in a way that a millivolt signal or a raw potentiometer output does not. A live-zero at 4 mA also means a broken wire reads as a fault rather than as zero wind.

Construction is UV stabilised plastic with stainless steel and anodised aluminium fittings. The plastic body is deliberate rather than a cost decision: it is non-metallic, so there is no galvanic corrosion at the fittings, and it is unaffected by the sunlight that degrades ordinary plastics. It installs on standard 1-inch IPS pipe like the rest of the range.

The point to settle at design stage is the safe-area side. An intrinsically safe sensor is only intrinsically safe as part of a certified loop, which means the barrier or isolator, the cable parameters and the earthing all form part of the assessment. Supplying the sensor alone does not deliver a compliant installation, so we specify it with the loop it belongs to.