How to measure water hardness electronically

Don M

Was wondering if there is a sensor made for this sort of thing or if something could be made "home brew"? For those that are versed in this matter- school me please. Was thinking of building a device that measures water hardness before / after water softener.

skylight

This might help you? http://www.globalw.com/support/hardness.html

Don M

skylight wrote: »

This might help you? http://www.globalw.com/support/hardness.html

Thanks but yes I already found that.

Duane Degn

I doubt you'll be able to do this electronically. There's just too many things that can affect the conductivity of water to measure the hardness based on the conductivity. I wouldn't be surprised if the conductivity stayed pretty much the same after the water has gone through a softener. The softener is just swapping sodium ions for the calcium ions and both make the water conductive.

It might be possible to perform some sort of spectroscopy on the water but I don't know what wavelength you'd want to use (this can be looked up of course).

Don M

Here's some examples of electronic testers:

http://www.hannainst.com/usa/prods2.cfm?id=042005&ProdCode=HI%2098202

http://www.tdsmeter.com/products/zt2.html

http://www.tdsmeter.com/products/ec3.html

Thought it might be a neat project with a Prop, some sensors and an LCD display...

Duane Degn

Don M wrote: »

Here's some examples of electronic testers:

http://www.hannainst.com/usa/prods2.cfm?id=042005&ProdCode=HI 98202

http://www.tdsmeter.com/products/zt2.html

http://www.tdsmeter.com/products/ec3.html

Thought it might be a neat project with a Prop, some sensors and an LCD display...

Thanks Don. I didn't know about those.

I wonder how they work.

Don M

Here's another interesting page. About 3/4 down the page it mentions the tests for measuring hardness.

http://www.ausetute.com.au/waterana.html

Mark_T

It mentions selective electrodes - as I understand it these (like a pH meter) use an electrode made of the metal in
question (or an amalgam?) and a membrane permeable only to the ions of interest. The potential of such an
electrode has a concentration dependent term - in other words the potential is a proxy for the log
of the equilibrium constant for the reaction M+(aq) + e- <--> M(s)

The tricky bit is finding a suitable membrane for a particular metal I believe.

Wikipedia seems to bear out my memory here: http://en.wikipedia.org/wiki/Ion_selective_electrode

LoopyByteloose

i suspect that the biggest problem with direct electrical measurement of water hardness might be that the calcium in the water would begin to electro-plate the surfaces of the electrodes involved. Once that process begins, readings are likely to make little sense.

I suppose one could set up a device that cleans the electrodes before each reading, but it begins to get complicated.

As you can see above, the use of a membrane to isolate just the ions you want to quantify may be necessary, and you still have the problem of keeping the electrodes clean.

RS_Jim

Analog Devices makes a chip the AD5933 that measures impedance by measuring electrical conductivity of a liquid. I believe that with the proper electrodes and software this could be made into a water hardness measuring device.
Jim

Mark_T

but conductivity doesn't measure hardness, as has been mentioned.

RS_Jim

The 5933 measures the ec of the test liquid with different frequencies of signal looking for resonances and measures each signal. It is more than just applying a simple voltage and measuring the drop.
Jim

wass

Here's a commercial version of what you want: http://www.spectradyntech.com/products/akms.htm
Seems like it would be quite an interesting DIY project.