Schaevitz® LVDTs: Helping to Control Electric Power  
 

Giant turbines are made more efficient through precise regulation of transfer valves, which are best controlled by LVDTs.  Right angle Schaevitz® LVDTs can be seen in the lower right corner of the photo.

Schaevitz® LVDTs and RVDTs have been used for valve control by the largest steam and gas turbine manufacturers since the late 1960's. Schaevitz®, now manufactured by Measurement Specialties, has been contracted by power generation industry leaders to make original and certified replacement parts.

Since power generation turbines were first built, engineers have tried to make them more efficient. Valves such as stop valves, control valves, inlet guide vanes (IGVs) and transfer valves regulate the circulatory system of steam and gas turbines.  Controlling flow through these valves is the key to increasing turbine efficiency.

The problem engineers found when looking for a sensor to measure valve position was the harsh environment on and surrounding the turbine. Temperatures may reach 400ºF. Gaseous vapors classify the area as intrinsic and require all electrical products to have Factory Mutual and/or ATEX approval. Describing the area as “dirty” is an understatement. Valve stroke can vary from less than an inch to 20 inches and some units, like ball valves, rotate instead of opening linearly. Furthermore, there are heavy vibrations during start up and normal operation.

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Introducing Model DP86 for Wet-Wet Differential Pressure  

The Model DP86 pressure sensor is used for differential pressure sensing in liquids or corrosive environments.

Measurement Specialties is pleased to introduce the Model DP86 sensor for measuring differential pressure in wet-wet applications.  The DP86 is designed for high performance, low pressure applications where differential pressure is required.

The DP86 is a double-sided, media compatible, piezoresistive silicon pressure sensor packaged in 316L stainless steel housing, which makes it suitable for use in liquids and corrosive environments.  The Model DP86 is built on the size template of Measurement Specialties’ popular Model 86 pressure capsule, which matches a common size used in industry.  The product is designed for O-ring mounting, with silicone oil transferring pressure from the stainless steel diaphragm to the sensing element.

Model DP86 differential pressure can be used for measuring tank liquid level.

The DP86 uses Measurement Specialties’ UltraStable die for long term stability and reliable performance.  Seven different pressure ranges are available, with a low-pressure model (0 to 5 psid) and six other ranges from 0 to 15 up to 0 to 500 psid.

Wet-wet differential pressure sensors are typically used for OEM equipment where corrosive gas or liquid level needs to be controlled. Common applications for the DP86 include tank level measurements, liquid and gas flow, water management, process control systems, hydraulic systems, filtration, refrigeration, compressors and aerospace.

The advantage of using a differential pressure sensor instead of two gage sensors for measuring fluid flow is that accuracy is always specified as a percentage of the sensor's full-scale reading. By using a differential pressure sensor, the full-scale reading can be much smaller, thereby reducing measurement error. A differential pressure sensor can also be used as a gage sensor inside a closed test chamber (since the reference port is closed to the environment).