KKM 740 - Kabel-Kapazitäts-Messgerät
- Field measurement of cable capacities resistant to interference
- Handheld measuring instrument for fast and easy application, usable either with mains cable, batteries or rechargeable batteries
- Capacity measurement via AC voltage 30 V eff., galvanically isolated
- Measurement range 0 … 999 nF
- Digital measurement display
- Max measurement error ± 1% of reading ± 1 Digit
- High suppression of interference voltages
- Constant monitoring of interference voltages
- Unearthed measurement circuit
Merkmale
The KKM 740 was designed to measure the capacity of a single line within a multi-core cable against EARTH and neighbouring lines.
Especially measuring laid cables is highly influenced by interference voltage and interaction with parallel live cables. Common measurement methods using low sinusoidal voltage levels or similar characteristics result in huge measurement errors or even complete uselessness of the measurement.
To eliminate most of these problems, the KKM 740 uses high voltage levels, high frequency and special preparation of the measured signal.
The input impedance of an open line is calculated like following:
ZL = R / jwC × coth RjwC × l ;
with R = resistance (e. g. 20 Ohm / km), C = capacity (e. g. 100 nF / km) and l = length of line. For selection of the frequency the measurement error due to line resistance was considered to be negligible.
A very important characteristic of KKM 740 is the fact that the device only considers the signal it has sent itself for measurement. All other interferences will be ignored.