Malvern Visco 88, User Manual, Page: 31 / 74

Making a measurement Chapter 3
Visco 88 Page 3-9
3.
While supporting the viscometer’s weight, loosen the viscometer clamp. Ease
it down until the top of the gap adjustment screw fits into the hole in the vis-
cometer clamp.
At this stage the gap between the measuring systems should be about 5mm.
4.
Slowly lower the measuring system by turning the adjustment knob

on the
bottom of the thread clockwise until the gap is almost touching the lower plate.
(Turning this knob anti-clockwise increases the gap.)
5.
Adjust this to give the required gap. “Zero in” on a feeler gauge of the correct
size then remove the feeler gauge.
6.
Hand tighten the lock nut

so that the gap adjustment screw cannot move.
Check the gap again with the feeler gauge and readjust if necessary.
Parallel plates
For parallel plates set a gap of 0.5mm, 1mm or 2mm, as given in the table in Chap-
ter 2 , using a feeler gauge of the appropriate size.
Other measuring systems
Cones of other angles should have certification showing the truncation height.
Follow the above procedure with a feeler gauge of this size.
Other measuring systems will be supplied with specific gap setting instructions
when purchased from Malvern Instruments.
Optimising the measurement system
This procedure checks that the measuring system is suitable for the viscosity of the
sample loaded. It involves reading the torque value at the chosen rotational speed.
Note
If the torque is below 0.5mNm, use a more sensitive measuring system
(larger diameter/surface area) or choose a higher speed. If the torque is
above 9.5mNm, use a less sensitive measuring system (smaller diameter/
surface area) or choose a lower speed.
To optimise the measuring system:
1.
If using cone and plate or parallel plates, lower the upper system until it stops at
the set gap.
2.
Press the START button to start the motor at the chosen speed.
3.
Press the FUNCTION button until the torque, M , appears on the display.
i