About Cable Height Meters
Suparule Cable Height Meter Application Note 1:
The Cable Height Meter must point directly at the cable in question because Suparule Cable Height Meter operate on the speed of sound principle; the meter sends out an ultrasonic signal (ie. a sound wave which is above the human hearing frequency range). The cable height meter then measures the time it takes to receive the echo of that sound signal, after it has bounced off an object, ie. the cable being measured.
Using the speed of sound through air equation, the cable height meter can then accurately calculate the distance traveled by the signal within the time recorded, and therefore the distance from the meter to the object being measured.
The ultrasonic signal originates from the ultrasonic transducer positioned at the center of the cone of the cable height meter. The physical area covered by the signal beam spreads out as the signal moves further away from the meter. The exact width of the signal beam at a particular distance from the meter is detailed in the performance diagrams at the back of the cable height meter user manual and datasheet.
For example, at the transducer the signal beam width is approx. 16mm, while at a distance of 10m from the unit, the beam width has increased to over 1m.
When the ultrasonic signal reaches an object, such as an overhead cable, the signal will bounce off that object. After it has sent out the ultrasonic signal, the meter waits to receive the signal which has bounced off the object being measured. However, in order for the meter to pick up the bounced echo, that echo signal must be directed back to the cone of the meter. If the signal does not travel back to the cone, then the meter will never see the echo, and therefore cannot calculate the time and distance travelled.
Referring to figure 1, it can be seen that, if the cone of the cable height meter is not pointed correctly at the object (eg. position A), the transmitted signal will bounce off the object (in this case a sloping wire) at such an angle that it will not return back to the meter. This will result in an invalid or null reading. In order to ensure the signal echo returns correctly to the cable height meter, the unit must be positioned such that the face of the cone on the meter is parallel with the object being measured (ie. position B).
When measuring sloping wires, it is necessary to have an idea of the direction of the slope of the wire. Position the meter with the back of the cone touching the ground, and the face of the cone pointing in the general direction of the wire. Tilt the Meter sideways and/or back and forth, still keeping the back of the cone on the ground, until a valid reading is received.
Note: when measuring multiple cables, they must be parallel to each other to ensure the meter "sees" them. If one or more of the cables has a different slope, then using the same theory described above, the echo returned from that cable may not reach the Meter, and therefore give a null or invalid reading.
Suparule Cable Height Meter - Measures More Than Just Cable Heights Application Note 2:
The standard Suparule CHM 300 and CHM 600 products are primarily designed for use by Utilities and Telecom personnel for the measurement of the heights of up to six overhead wires. However, the instrument can also be used to measure the height to many other overhead items, such as bridges, tunnels, canopies, etc.
Prime markets include utilities, telecoms, and cable T.V. installers. The Cable Height Meter is vital in establishing and maintaining adequate clearance and required spacing for various cables, whether individually strung or carried on common poles... but its usefulness doesn’t stop there.
Heavy construction is another industry that can utilise the features of a cable height meter. The movement of heavy equipment into, out of, and around construction sites is a high-risk exercise and must be heavily safety oriented. There are regulations and mandated safety practices intended to protect workers from accidents particularly associated with the movement of heavy equipment. Most critical are cranes, derricks, and similar equipment that possess long booms. It is all too easy to become preoccupied with the physical problem of positioning the massive and bulky main body of such items and momentarily forgetting about the long, protruding boom.
Zap! The boom strikes overhead power lines and the crane becomes part of a massive short circuit to earth. Many terrible and lethal accidents have occurred in this fashion and these have been taken into account in delineating vital practices. Among these is a requirement that a warning sign be prominently displayed on the approaches to any power line crossing over access routes or work areas where equipment bearing a boom may be moved or maneuvered.
Vital information on these signs includes the minimum clearance (at point of greatest sag), which the boom must be able to clear by at least three meters. The construction company must have a convenient and reliable way of measuring and checking these.
What better answer to this challenge than a cable height meter? Just stand under the cable and press a button. Within minutes, the minimum clearance can be reliably located and measured.
If you have any questions contact our friendly team today - experts are here to advise on the full range of cable height meters.