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simpleSDI™ vs AutoSDI®

A comparison between two portable, automated Silt Density Index (SDI) test tools.

Ease of use




Sort of. Requires 110 or 220 VAC within 6 feet of the meter to operate.

Yes. Battery powered so tests can be conducted anywhere there's a water supply. Operates up to 13 hours per charge.

Regulator maintains consistent pressure?

No. The regulator is not linear accross the range of flow encountered in a typical SDI test. This will require the operator to monitor the system during testing in order to maintain a consistent 30 psi.

Yes. The simpleSDI regulator is very linear across the entire flow range. Only simpleSDI provides true "set-it and forget-it" operation.

Easy to use membrane filter housing?

No. The filter housing is embedded in the surface of the meter. Opening and closing the housing can be very difficult. Water spills on the surface of the meter each time the housing is opened.

Yes. The in-line mounted housing allows easy access. In normal use, the housing is positioned away from the surface of the meter so that water does not spill on the surface of the meter.

Air bubbles easy to purge?

No. The vertical orientation of the filter housing makes it difficult to purge air bubbles. An air bubble trapped at the membrane surface invalidates the test requiring a time-consuming retest. High loss plumbing design makes it difficult to purge air from the system.

Yes. The filter housing can be oriented in any position to facilitate clearing the housing of air bubbles. Transparent tubing feeding the filter housing eliminates guesswork by showing if air bubbles are present. High flow plumbing design makes it easier to purge air from the system




Can the filter cake be inspected?

Sort of. The position of the filter holder makes it impossible to remove the membrane without disturbing the filter cake. Inspection of the filter cake can reveal important information to knowledgeable testers.

Yes. The inline design of the filter holder was conceived in part to allow the housing to be opened and the membrane removed without disturbing the filter cake. This feature was requested by a leading expert in RO system troubleshooting.

Covers full range of SDI tests?

No. AutoSDI performs only the SDI15 test (500ml sample size only). AutoSDI claims a range of 0-6.7. However, since, AutoSDI returns an error message when the test results indicate greater than 75% plugging (SDI15 of 5) the range is really only 0-5. On high SDI waters AutoSDI wastes your time with meaningless error messages.

Yes. simpleSDI performs SDI5, SDI10, and SDI15 tests on 100 and 500ml samples and displays the values for all 6 tests at the end of testing. simpleSDI delivers meaningful measurements on even the highest SDI waters.

Low pressure operation?

No. The AutoSDI meter requires 65 psi of feed pressure to conduct a test.

Yes. simpleSDI can operate successfully with as little as 35 psi feed pressure.




Rugged Case?

No. The case has thin .050” walls. The case is relatively flimsy and easily cracked. Definitely not crush proof.

Yes. Rugged, crush-proof case has a wall thickness 4 to 5 times that of AutoSDI.

Sealed Electronics?

No. The electronics are housed behind the overlay in the lid of the unit. The flexible nature of the plastic and the large seam area makes sealing of the electronics very questionable. The original AutoSDI unit had numerous field failures due to electronics damaged by water. This design may have been improved in the new unit.

Yes. The electronics are housed in a rigid, dedicated enclosure. The enclosure assembly has been tested by immersion underwater and found to be leak free.

Gold plated contacts?

No. Standard tin plated contacts throughout are susceptible to corrosion.

Yes. All of the electrical connectors feature gold plated contacts for improved reliability and freedom from corrosion.

Modular Construction?

No. AutoSDI's unitized construction makes service almost impossible. Neither the electronics nor the hydraulics are field serviceable.

Yes. simpleSDI was designed with serviceability in mind. Modular construction makes field service quick and easy.

Product Support



AutoSDI is a very small product for a very big company. When Osmonics discontinued AutoSDI in mid-2000 they also reportedly stopped providing parts or service for the meters already in the field. We can't predict the future, but past actions speak for themselves.

simpleSDI is our primary product. Accordingly, the success of simpleSDI and the positive experience of our customers is our primary concern. We are committed to providing the best product and the best support possible – today and for years to come.

AutoSDI® is a Registered Trademark of Osmonics Inc.
simpleSDI is a Trademark of Spears Design and Consulting Inc.