Advanced Instruments 4250, User Manual

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Immerse the tip of the probe into a container of ice and water
(~0°C). The resistance should rapidly increase to a range of
5500 - 6100 ohms.
With the tip of the probe immersed in a concentrated NaCl solution
(do not wet the probe leads or connector with the salt water), the
resistance between either probe lead and the solution should be
greater than 20 megohms. Carefully rinse the probe clean following
this test.
Probe damage is indicated by any deviation from the resistance para-
meters given above.
If sample probe replacement is indicated:
6. Loosen the two setscrews (Figure 10, Item 2) holding the mandrel in
the head chassis. Lower the probe and mandrel down over the stir
wire.
7. Fit a new sample probe by pushing the probe connector and wires up
through the hole in the head chassis before seating the mandrel.
Then raise the mandrel up around the stir wire. Align the mandrel so
the stir-wire channel is perpendicular to the front edge of the chassis
and so the flange is flush, with no gaps between the flange and the
underside of the chassis. Retighten the two setscrews to hold the
mandrel in place. Do not overtighten-overtightening will damage the
mandrel.
8. The probe length is factory adjusted to the mandrel, and should not
require further adjustment. Proper positioning of the probe and stir
wire can be quickly confirmed with the probe and stir-wire align-
ment tool provided with the instrument, or the method described in
the “ Mandrel, Probe, and Stir/Freeze Wire Alignment ” section shown
later on in this chapter.
9. Reconnect the probe connector on the head chassis, taking care once
again not to touch or bend the connecting pins.
10. Arrange the leads so that they will not touch the clapper (Figure 10,
Item 3) or be pinched when the head cover is replaced.
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Troubleshooting & Service