Viscometers and Rheometers

MDR 2000 front view

MDR2000 top die
When closed, the MDR2000 upper die (above) and lower die (below) enclose a radially corrugated test chamber roughly the size and shape of a two dollar coin.
MDR2000 bottom die
This article describes two types of machines used by a client of mine in the rubber industry. I'll briefly describe the principle of operation and also the differences between the machines.

operation basics

The MV2000 and MDR2000 are laboratory instruments from Apha Technologies. My client operates an array of these machines to evaluate a constant stream of rubber samples from their production facility. They are indispensable for quality control.

Simply stated, these machines apply heat and mechanical stress to a rubber sample held in a tiny chamber. The sample's resistance to stress — its stiffness or viscocity — reveals crucial information about the rubber formulation.

The MV2000 and MDR2000 are similar in size and appearance. Both feature a platen that lowers and raises pneumatically in order to seal and unseal the test chamber so that samples can be inserted and removed. However, the stress applied by the MV2000 is in the form of a continuous rotary stirring motion, whereas the MDR2000 twists the sample slightly back and forth in reciprocating fashion.

In both cases the objective is to measure the sample's resistance to the applied stress, and for this reason both the MV2000 and MDR2000 have load cells built into the drive mechanisms that apply the stress. The load cells are the heart of the machine, but they would be useless without the surrounding systems. For example, the PID heater logic and calibrated RTD temperature sensors are crucial to producing reliable, reproducible results. Safety interlocks and a transparent shield, raised by a reversible motor, protects the operator from injury. Finally, the microprocessor and peripheral boards manage operator input, administer the test protocol, process the test results and issue reports via serial link.

the controls

The "brain" of the machine is an 8" by 11" multilayer PCB which accommodates an 80188 CPU/peripheral IC and various analog and digital support functions. The same PCB is used by both the MV2000 and MDR2000 although of course the firmware differs. Also common to both machines are an Operator Interface board featuring pushbuttons and a Vacuum Flourescent Display, and an AC I/O panel with fuses, Solid State Relays and optocouplers.


The service issues I've dealt with so far have been similar to those with almost any industrial equipment. Assemblies that have moving parts eventually prove vulnerable to wear and tear, and the presence of electronic controls almost guarantees trouble from bad connections caused by dirt, oxidation and (especially) vibration and mechanical damage.

io panel  IO board  cpu board
Servicing the Unserviceable
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