DODK-117 – Fault location sensor
DODK-117 is used for insulation damage control at gas\oil pipes and power cable lines. This sensor operates with the receiver (AP-019, AP-027) and exploits the principle of voltage difference.
Brief description DODK-117
DODK sensor consists of two measurement electrodes, connected with cable. One of the electrodes has a cable for connection to the receiver.
ATTENTION! The survey should be performed by two operators. First operator holds the receiver in one hand and the electrode in the other. Second operator holds only electrode. Electrodes should be held without any gloves to ensure good contact with the skin.
DODK-117 How does it work?
Protective insulation of cables and pipes is used for avoiding metal to earth contact. If this insulation is damaged, insulated conductor is shortened to the ground.
When tracing transmitter is connected to the utility and to the ground, alternating current leaks in the spot of insulation damage to the ground and returns to the transmitter. It creates step potential on ground surface. Search of defects can be performed on all supported frequencies, in active or passive mode.
While using the DODK the evaluation of voltage difference is performed without direct contact to the ground. During the survey the operators hold the electrodes and move alongside the utility at the distance of cable length between each other. When one of the operators is standing above the damage spot, the receiver will indicate the maximum possible voltage difference.
Method of fault location using the DODK-117 sensor
Firstly, when locating the damage spot in MAX mode, one operator should stand above the utility and the second should stand as far as possible in perpendicular way to the utility axis.
Secondly, electrodes of DODK, carried by operators should be held without gloves to ensure good contact with skin. Further, measurement can be carried out on the go. Moreover, the signal level will slowly increase while one of the operators is approaching the damage spot. In addition when the spot of damage is passed by one of the operators, signal level will decrease. See pic. 1.
In conclusion, MAX method allows to locate the presence of the damage, however it is not too precise in localization of the spot.
Fistly, in this case both operators stand above the utility axis in the distance of the DODK cable. Secondly, while one of operators is moving to the damage, the signal will slightly rise then significantly decrease to the minimum. Further, then it will rise again while one of the operators is passing the damage. Moreover, the spot with minimal signal level indicates the damage. See pic. 2.
In Conclusion, DODK-117 sensor offers more fast but less precise way for fault location than DKI-117. DODK sensor allows to survey longer pieces of cable which makes usage of DODK for bigger spots first and then DKI for smaller areas more rational.