MREL MicroTrap - 4.7 Probe Resistance Out Of Range Lights

MicroTrap™ Operations Manual - Edition 4.4
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If no more experiments are to be conducted and the data storing process has been finished (St e p 11 above), then the data are ready
to be transferred to a computer using the DAS™ Data Acquisition Suite Software. If data transfer is to be conducted later, then the
MicroTrap™ VOD/Data Recorder can be switched OFF and the data will remain in the MicroTrap™ VOD/Data Recorders non-volatile
memory.
4.7 Probe Resistance Out Of Range Lights
There are two OUT OF RANGE warning lights on the MicroTrap™ VOD/Data Recorder. One is labeled , which illuminates when the total
resistance (resistance VOD sensor plus coaxial cable) is greater than 3,000 ohms. The other is labeled , which illuminates when the
total resistance is less than 50 ohms. The MicroTrap™ VOD/Data Recorder is designed to only perform VOD tests using this range of initial
resistance values (50 – 3,000 ohms).
There are three reasons for the initial total resistance to be LOW:
1. A short circuit somewhere in the coaxial cable and probe assembly, including any BNC connector(s) or BNC Adapter;
2. A damaged PROBEROD;
3. An insufficient length of PROBECABLE.
Item 1 can be tested using a Blaster’s Galvanometer to test the resistance/continuity of the coaxial cable and probe assembly. It can be
and solved by remaking the connections or replacing faulty BNC Connectors. Item 2 is addressed by replacing the damaged PROBEROD.
If Item 3 can be addressed by attaching some additional length of PROBECABLE to the probe circuit. This will not affect the VOD results. If
PROBECABLE-LR is being used in the test, then consider using PROBECABLE for such tests in the future. The unit resistance of PROBECABLE
is approximately 3 times that of PROBECABLE-LR.
There are three reasons for the total resistance to be HIGH:
1. An open circuit somewhere in the coaxial cable and probe assembly, including any BNC connector(s) or BNC Adapter;
2. A damaged PROBEROD;
3. Too long a length of PROBECABLE.
Item 1 can be tested using a blaster’s galvanometer to test the resistance/continuity of the coaxial cable and probe assembly. It can be
and solved by remaking the connections or replacing faulty BNC Connectors. Item 2 is addressed by replacing the damaged PROBEROD.
If Item 3 is the cause, then reduce the length of the PROBECABLE used in the test by cutting out excess PROBECABLE between holes
and remaking the connections using the wire cutters and electrical tape. Alternatively, this can be achieved by reducing the number
of holes being recorded by cutting the PROBECABLE and remaking the appropriate connection with the wire cutters and electrical
tape. If PROBECABLE is being used in the test, then considering using PROBECABLE-LR for such tests in the future. The unit resistance of
PROBECABLE-LR is approximately 1/3 that of PROBECABLE.
CAUTION
The continuity mode of commercial multimeters may apply a higher current than is allowed at a blasting site. Any
tests with continuity mode of a multimeter should be done with cables which are in a non-blasting field location. If
the VOD sensor is in the vicinity of energetics, it is recommended to use a Blaster’s Galvanometer to measure the
resistance values.