Well, some might know and some might have guessed that it is an invention of Reverence George Dobbs G3RJV. George found that he was constantly going to rallies and seeing meters that he could not check or determine their sensitivity. So he designed the Tripus which have taken on stage further by adding another cell, thus enabling it to check LEDs and seven segment displays.
This simple unit consisting of two cells, four resistors and three crocodile clip on leads which are all held together with tape.
The circuit diagram shows the unit works. When the Black and the Red leads are shorted together, 10miliamps flows across the circuit and when the Black and Yellow leads shorted together,100 microamps will flow.
When testing meters, start with the Black and Yellow leads and if the meters reads half scale the movement sensitivity is 200μA FSD(Full Scale Deflection). If the meter flies over to FSD it is more sensitive than 100microamps, but as the most sensitive meter that you are likely to find will be 50microamps, the meter should not be damaged.
If the meter hardly deflects at all, then its sensitivity is obviously low, and this is where to 10miliamp Red lead can be used! The result obtained enables the sensitivity to be estimated in the same way as with the Yellow lead.
For testing LEDs we use the 10mA lead and this could be enough to illuminate all colours if the battery is fully charged. We can also tell if seven segments displays are common anode or common cathode, as we know the polarity of the battery within the Tripus.
For charging my Tripus, I clip the Black and the Yellow leads onto my nicad charger and charge in the normal way for the cell size used.
And why is it called the Tripus?
Well, it only has three legs!
Ian Keyser G3ROO/Radcom 9402/sv3auw
Μια μικρή και εύκολη κατασκευή για τον έλεγχο των οργάνων και LEDs τα οποία εμφανίζονται στα ham-οπάζαρα.
Ζωντανά ή πεθαμένα!