The CHM Series of cable height meters use ultrasonic sound to determine the height of up to six overhead cables and wires. These instruments are designed to address specific measuring requirements on cables up to 75 feet (23 m). The CHM600 (C/N 659600) and CHM600E (C/N 659600E) are designed primarily for power cable applications, while the CHM2000 is designed for telecommunication applications.
These cable height meters emit short bursts of sound which originate from the cone-shaped transmitter. The microprocessor in the instruments calculates the elapsed time for the bursts of sound to be reflected from the cable back to the instruments. The result can be displayed in either feet and inches or meters. However, before the final measurement can be displayed, the air temperature must be measured because the speed of sound varies at approximately 0.2 percent per degree Celsius.
A temperature sensor, mounted at the front of the instruments, senses the actual air temperature. This information is sent to the microprocessor and incorporated into the algorithm. The distance is then displayed in meters or feet and inches, depending on which was selected.