Comparison of Servo Gauge with Radar Level Gauge

  • Thread starter Aalhad & Ashok Saraf
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Aalhad & Ashok Saraf

I would like to know what are the advantages of Servo Gauge type level measuring instrument over noncontact Radar type level gauge, especially for level gauging for the low viscocity petroliums/oils .

I would be interested to know if any of the list members can provide some experience about different types of level gauges and their merits.

Ashok Saraf
Syslab Automation Pvt. Ltd.
Pune India
[email protected]
There are four basic types of Radar Level Gauge:

First, is the low-accuracy pulse radar units, such as those made by Endress+Hauser, Siemens/Milltronics, and Ohmart/Vega. Now these are only "low accuracy" when compared to units designed for tank farm gauging. These are excellent general purpose radar units, but they are limited in use to materials with dielectric coefficients greater than about 8 or so. It
generally rules them out for low viscosity hydrocarbons. Too bad, too, because they are very inexpensive.

Second is the various radar-by-wire designs, such as Alliant(Bindicator-Celtek) and Magnetrol, etc. These are mostly used for solids, but could be used in hydrocarbons. They are also relatively

Next are the FMCW units, such as those made by TN Technologies, Krohne, the less-expensive units made by SAAB, and the one that Daimler-Chrysler makes for Fisher Rosemount. These are moderately high accuracy, and can be used in gauging fluids with a dielectric of 3-5 or so. The compromises made in the designs of these units in order to make them look through small (4"<100 mm> to 6" <150 mm>) vessel ports reduces the accuracy and the ability of these units to see lower dielectric constants. These are designed as
process gauges, not tank farm designs.

The highest level of accuracy are the units designed specifically for Tank Farm Gauging, such as the big SAAB units and those made by Enrauf...they were designed to compete specifically with servo gauges and with hydrostatic level gauging and are designed to be used specifically for tank farms. These gauges consistently outperform their competition but are very expensive.

Take your pick,

Walt Boyes

Applications Columnist, _Flow Control_ magazine

and currently in the "out of work" state....

Walt Boyes -- MP Consultants
[email protected]
21118 SE 279th Place - Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office

Bertrand Callens

Another option might be to use laser technology.

Optech used to provide a laser level monitor called Sentinel 3100. I never had the opportunity to use it, but it should be ok to measure levels for a wide range of products, either liquids or solids, without being affected by vapor layers, steam, dust, etc..

This branch of Optech has been acquired by TN
Technologies/Kay Ray-Sensall ( and you can contact them to get further information

Bertrand Callens
Emtrol, Inc.
I am using both servo based and radar based level measurement instrument for our refinery and oil terminal Tank farm . I always found level difference between these two types of instruments .There is always a difference of + - 8 mm .Expert says radar is more accurate. It is confusing to compare both at site. Lab test & analysis is always preferred .