Audible Alarm; Influence Of Grounding Resistance Of The Auxiliary Rods; Special Considerations About Grounding Resistance Measurements - TENTECH MTD 20KWe Manual De Uso

2.11. Audible Alarm

The MTD20KWe has an audible alarm circuit to avoid false measurement
records. If, due to any reason, the current is lower than the value required
to perform reliable measurements, or if there is no current flowing
between H and E, the alarm circuit will be activated and will emit an
audible intermittent signal. When the operator is in the field during
measurement and hears the intermittent "beep" sound, he must check the
connections to the rods and to the earth tester terminals, as well as the
wires continuity (possibly, a wire may be cut off). If there isn't any
abnormality in the connection or in the wires, it is possible that the soil
resistance is abnormally high, causing an excessively high diffusion
resistance of the auxiliary rods. That resistance could be improved by
watering the auxiliary rods, or by inserting several interconnected rods.
The battery status must also be checked.
2.12. Influence of grounding resistance of the
auxiliary rods
Whenever the probe grounding resistance is lower than 1,000 Ω, the error
caused is not significant (less than 5%). The current rod may have a
resistance of up to 5,000 Ω, without affecting measurements and without
causing significant errors.
2.13. Special considerations about grounding
resistance measurements
By employing the Fall of Potential method, normally used to measure
Grounding Diffusion System (GDS) resistance, two rods are used as
auxiliary electrodes. In figure 01, D is the distance between GDS E and
1 1
the E current electrode, whereas D is the distance between GDS and
3 2
the E probe The current generated by the equipment flows through GDS
2 .
and the current electrode, and the voltage between GDS and the E
2
probe is measured. The R value is obtained as the quotient between the
voltage and the current.
In figure 05 the potential profile has been graphically shown relating the
GDS in the area between this and the current electrode, assuming that
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