This article applies to: All cone/plate viscometers with a version 1 tension arm mount.

This article outlines the short procedure required to adjust the setting of the tension arm that holds the sample chamber in place on cone-plate laboratory viscometers. This procedure can be used for minor tension adjustment, or if the tension arm is significantly too loose or too tight.

Required Materials

• Phillips head screwdriver (Size #1 or similar)

The problem

Sometimes your viscometer may come back from service, or you might start using a newly purchased spindle and chamber combination, and you may notice that the tension arm does not hold the sample chamber well or at all, or it is simply too tight to install properly. This can be due to slight differences in the heights of spindles and sample chambers, either the new set you are trying to use, or the master set used for calibrating your instrument after service.

On the left below is an extreme example of the tension arm being too loose and not holding the sample chamber in place. On the right below is the counter-example of the tension arm being much too tight to install properly.

Open

Open

Adjusting the tension arm

To adjust the tension arm, we first need to set the gap adjustment ring to roughly the proper location for obtaining a proper gap. Install the spindle on the instrument, and from the configure viscosity test screen, select “Set cone plate gap” (on a DVNext), or flip the gap adjustment switch on (on a DV2T, DV3T, or older instruments).

• Swing the tension arm out of the way for now. Place the sample chamber on the instrument, and apply a small amount of upward force to hold it in place against the gap adjustment ring.

• Adjust the ring until the gap indicator shows yellow on the screen (DVNext), or the yellow indicator light illuminates (DV2T, DV3T, others).

• Put the sample chamber aside, and turn off and unplug the instrument. Turn the instrument around so that the rear is facing you.

• Loosen, but do not remove the two Phillips head screws on the back side of the tension arm mounting block. See the image below for the location of these screws.

• The outer tension arm tube should now be able to be shifted up or down depending on the adjustment required. It may be easiest to gently twist the tube and apply gentle upward or downward pressure for precise adjustment.

• Adjust the tension arm tube until the surface of the tension arm is 2 to 3 millimeters above the bottom surface of the sample chamber. You can hold the sample chamber up to the instrument to check alignment. Below is an image of a good tension arm position.

• Once the tension arm is in an adequate location, gently tighten the two Phillips head screws. Do not over-tighten the screws, and be careful not to strip the heads! The tension arm mounting block does not need much tension to grip the tension arm tube very tightly.

The tension arm should now properly hold your sample chamber in place. You may need to occasionally perform slight adjustments when switching between different sets of spindles and sample chambers. This is not common, though, and requiring frequent major adjustments could indicate a larger problem.