We recently used guided wave radar probes from Magnetrol, 7E5 transmitters and 705 probes. These were specified to us and I was eager to see how they would work. These things were a monster to set up. Magnetrol said the Hydrated Lime we were using was not the right application, dielectric constant was too low. They sent a tech out to reprogram the transmitter. Now my problem is, what happens when the client has to replace this item?

As far as Hydrated Lime, Soda Ash, etc, Ultrasonics work fine except when you are loading chemical. I've seen people blow low pressure air to keep the dust off. Good for keeping up with inventory, not for metering product flow.

Jeff

Jeff,

Thanks for your comment. I have taken a quick look at the manufacturers' data based on the name and models you provided. I think I see what might have been a potential problem.

The probes for bulks solids as listed in the Magnetrol brochure are the 7X2 and 7X5. Are these what were used? The brochure indicates the minimum dielectric that can be measured using the single cable 7X2 is 4.0 and the minimum dielectric for the 7X5 twin cable is 1.9. These specs are pretty high, especially the one for the single cable which is typically the most common probe used for solids because the twin can have bridging problems.

Hydrated lime usually has pretty good dielectric constant. For example, one manufacturers list the dielectric for hydrated lime at 4.8 and for "lime" or "slaked lime" at 2.0. Unfortunately the dielectric constant of a material can change and can be slightly different depending on the sample and also depending on how packed or loose the sample is that is measured. I think a dielectric of from 2 - 4 is pretty accurate and that should be adequate for guided wave radar technology that is engineered for solids applications.

That being said, when considering the dielectric of the lime and the spec of the product you used, I think that what you were told by Magnetrol is correct, the dielectric constant of the material is too low for their unit. If they sent a tech out and got it working for you, great! Perhaps they adjusted the gain or threshold setting I do not know. I do know that there are other guided wave radar units with rugged single cable probes that off-the-shelf will measure materials with dielectric constants easily down to 2.0 and will measure lime at 2.0 to about 50-60 ft and hydrated lime with a dielectric constant of 4.8 to about 90 ft. There is a relationship between dielectric and measuring range. Look for an article in the April issue of Powder Bulk Solids magazine on how to ensure successful installations of guided wave radar devices as this is covered in that article. There will also be a post coming up on that subject at the Level Measurement blog at www.monitortech.typepad.com so you might want to check that out too.

I hope all this helps somehow. Give me a call if you want to discuss it further or need a solution for this and silimar applications (800-766-6486).

Joe

Jeff,

I just got some corroborating information on soda ash and the dielectric is about 2.5. Guided wave radar should work fine. Give me a call or email me if needed. Thanks.

Joe