Selecting the Right DP Level Device for the Temperature Conditions

With the season in change from summer to autumn here in the northern hemisphere, let’s look at differential pressure (DP) level measurement performance at various temperature ranges and particularly at cold weather performance.

This quick 2:35 YouTube video, DP Level Solutions Optimized for Cold Climates: Improved Response Time, highlights the importance of selecting the right technology and fill fluids depending on the temperature range of the application.

Traditionally for cold climate DP level applications, heat tracing has been required on the capillaries running from the process to the DP transmitter. Not only does this add expense, it adds complexity and expense to install and maintain. Without this heat tracing, the measurement response time can slow considerably or stops completely.

The video highlights an improved approach that eliminates the need for heat tracing and demonstrates cold temperature effects on fill fluid response times in a lab simulation environment. The simulation environment has 4 Rosemount 3051S DP Level transmitters:

  1. A control unit with a direct process connection
  2. A Thermal Range Expander with dual fill fluid remote seal
  3. A Silicone 200 fill fluid remote seal
  4. A Silicone 705 Fill Fluid remote seal

A manifold connects all 4 DP level devices together. The control unit transmitter measures process conditions directly and response immediately to pressure changes.

The transmitter with Silicone 705 fill fluid is best for high process temperatures up to 370 degC (698 degF). It has slow or no time response in colder temperatures below 20 degC (68 degF). The transmitter with Silicone 200 fill fluid is better for a broader array of applications with a temperature range from -45 degC (-49 degF).

The Rosemount 3051S Thermal Range Expander uses both Silicone 705 and Silicone 200 to serve applications in a temperature range from -45 degC to 410 degC (770 degF).

Beginning at just over the one-minute mark the video highlights the test conditions to show the response rates of all the DP devices to pressure changes. One test is performed at 20 degC (70 degF). The control responded immediately and the Thermal Range Expander and DP transmitter with Silicone 200 responded within 3 seconds. The transmitter with Silicone 705 took 30 seconds to respond to the change.

A second test was performed with the capillaries in an ice bath—0 degC (32 degF) with the same pressure change conditions. The response times for the first 3 were the same, but the response time for the one with Silicone 705 took 8 minutes.

If you’re process is in cold climate conditions, make sure to apply the right DP level transmitter to fit the temperature conditions.

You can connect and interact with other level measurement experts in the Level group of the Emerson Exchange 365 community.

Posted Tuesday, September 12th, 2017 under Level.

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