Many would believe that a balanced system, with its equal length capillary applied to both high and low side seal of the sensor is the optimum arrangement. Rosemount believes differently.
Rosemount's tuned-system approach has the DP cell mount directly on the high side, with a capillary to the low side seal.
Assume both systems incur an identical process and ambient temperature increase from original zero. Total system error equals the sum of temperature error and head error. Head error is always greater than temperature error. Both head errors are the same, as the distance between process taps is identical.
When evaluated in a scenario having 3" FFW-style seals on the tank with height difference of 3 m between taps, with the system zeroed at 20°C, installed in a 150°C process, with an ambient temperature of 37°C - it noted that the tuned system reduce errors by 10%, improves response times 80%, and actually costs 20% less to implement.
Savings in implementation come from the fact that no mounting bracket, mounting stand or excess capillary is required.
With regards accuracy
Balanced systems hurt performance:
* Only address temperature effect; yielding zero temperature effect errors.
* Do not address head error; fill fluid density changes as temperature changes.
(Head error is the largest system error.)
Tuned-systems improve performance:
* They compensate for head error.
* They yield a reduction in total system error.
* Improve time response by 80%.
* Improve total error by 10%.
(Value Proof 28 is available from Alpret Control Specialists - for those wanting more details).
The company also offers Instrument Toolkit, which allows users to specify a tuned-system and calculate the performance difference in their own scenario.
Tuned-Systems are offered as a standard design, available with virtually any diaphragm seal type and configured as either a direct mount or liquid level transmitter. Tuned-Systems are engineered exclusively by Rosemount.
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