rotational viscometer

[vmgobinath]

Hi,

I have to build a viscometer that measures viscosity . It will have to be a rotational viscometer..
I tried using the torque of a DC motor but unfortunately measuring torque of DC motor is very difficult. But only with some expensive torque sensor (~1000$) possible. But we are looking a cheap solution or any other method.

Any ideas about how to make...

 

[Beau Schwabe]

What if you apply a constant current and voltage to the motor and simply measured RPM?

 

[ronsimpson]

and simply measured RPM?

I think the RPMs must be constant for a rotational viscometer.
I think you need feedback to keep the motor constant. Measure the current in air, then in solution. Current2-current1 will have a function that gives viscosity.
Why the big money for measuring torque? Torque can be measured on the motor shaft, or the motor body or the container.

 

[Pommie]

To measure torque you could have a pivot bar that's rotated by the motor and presses against a load cell. You can get the load cells very cheaply from banggood. They range from 1kg to 50kg.

Mike.

 

[ronsimpson]

By looking at other rotational viscometers: some use a synchronous motor held constant speed by the power line. The solution container wants to turn. A simple coil spring keeps the container from turning too far. Watching how far the spring turns.
In this picture the spring in on the motor shaft but it could be in other places.

I like Mike's idea of load cell. You should be able to measure torque at the motor or the container.
---edited---
By looking at the price of meters it is clear no one will pay $1000 to measure torque. Not $100 but more like $10.

 

[Beau Schwabe]

Keeping the speed constant and measuring the load or current on the motor is probably the best approach, but going the other way would work as well ... by keeping the voltage constant to the motor dynamically under load and measuring the motors rpm would give a similar result.

 

[Nigel Goodwin]

My daughter spent a year actually using one - essentially it was a big food mixer, that heated the contents at the same time as it stirred, and printed out the data of how viscous the mix was.

It was to do with Vulcanization, she was employed as an intern for a year to try and find out how a new process (discovered by accident) worked, and involved trying the effect of different chemicals on the Vulcanization process, and the graphs from the mixer showed the actual effects.

As others have said, I would imagine it's mostly a question of measuring how much power the motor takes, the more viscous, the more power - another concern is overloading, and just like a Kenwood Chef this industrial one included a sacrificial gear, which sheared off when the pressure got too high.

So if this the type of thing the OP is wanting to do?, a kind of 'mixer', and would measuring the power to the motor be enough?.

 

[Diver300]

About 40 years ago, in a cement factory that is now a housing estate, I used a rotational viscometer.

It consisted of a geared induction motor, probably 3-phase, turning a flat disc in the slurry being measured. There were small, curved, radial ridges on the flat disk. The disc would have been at near constant speed. The torque was measured by measuring the reaction force on the motor.

It seems that measuring the reaction torque on the motor is the easy way to go.

 

[dr pepper]

For a prototype you could use an arduino with pwm controlling the motor, feedback from it to maintain a constans speed, then a bearing such as a vcr player head for the sample jar to stand on, then a load cell and something like a Hx711 load cell amplifier to i2c to measure the rotation force of the sampl jar,

 

[gophert]

Get a little power meter and measure the power needed to maintain a constant rpm.

 

[shortbus=]

For a prototype you could use an arduino with pwm controlling the motor, feedback from it to maintain a constans speed, then a bearing such as a vcr player head for the sample jar to stand on, then a load cell and something like a Hx711 load cell amplifier to i2c to measure the rotation force of the sampl jar,

Or do the same but have the load cell measure how much the motor moves. That way everything is in the head unit.

 

[ronsimpson]

Measuring motor current works but as the motor ages it will need calibrated. The load cell does not have old age problems.

 

[gophert]

Laboratory viscometers seem to need constant calibration vs a reference sample. Kind of like pressing the TARE button on a balance every time something is weighed.

 

[dr pepper]

I use a standard 'mole' solution to calibrate a tds gauge for coolant where I work, there is probably a standard viscosity solution for calibrating viscometers, it'd probably need to be used at a certain temp.