Model 86 PID
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The Mesa Laboratories, Inc. Nusonics Model 86 Pipeline Interface Detector (PID) is a third generation instrument that incorporates all the features and advantages made possible through years of experience in pipeline instrumentation. The Model 86 PID includes the proven reliability of Nusonics electro-acoustic transducer technology to give the ultimate in performance to meet exacting specifications for interface detection.
The Nusonics Model 86 PID determines liquid composition by measuring sound velocity, which is unique and repeatable for a liquid. The relation- ship between sound velocity, temperature and pressure is different for every liquid. Once this relationship is known for a liquid, sound velocity can be used to monitor changes in liquid composition and interfaces between liquids in a pipeline with greater precision than with other measuring instruments. The Model 86 PID can detect small changes in liquid composition and interfaces between liquids that could otherwise be missed.
Applications
The Model 86 PID is utilized on new or existing pipelines and plants that need to detect interfaces between various liquids that are pumped through the same pipeline. The Model 86 PID is used in hundreds of sites throughout the world and has proven itself with a wide variety of products and situations due to its high sensitivity and fast response time.
Operation
The Nusonics Model 86 PID consists of a sensing probe assembly and a transmitter. The probe assembly is installed into the
pipeline.
It consists of a sound velocity transducer, platinum- resistance temperature probe and solid state pressure sensor. The probe assembly,
containing the three sensing elements, may be mounted into the pipeline on a 4" 6" or 8" ANSI 150#, 300# or 600# flange assembly as shown in
Figure 1. The length of the probe assembly can vary from 7.5" to 72" to meet the installation requirements.
Alternately, the probe assembly may be mounted in a probe retractor (Figure 2) with a 4''- 150#, 300# or 600# flange, permitting initial hot tap installation and withdrawal of the probe assembly without shutting off the flow or the pipeline. The probe retractor can be mounted on the user furnished 4" valve The unit is provided with 25 ft. cable (std) and maximum cable length can be up to 100 feet.
If the probe assembly is to be installed in a horizontal pipeline, it is advisable to install it within 45 degrees above or below the horizontal plane. This minimizes the tendency for entrained air bubbles to become trapped under the sound velocity transducer of the probe assembly. Pumps and other off line sampling schemes are not required with the Nusonics probe assembly, resulting in significant initial cost savings.
The Model 86 PID transmitter is mounted in a NEMA 4X enclosure with a window to view the keypad and LCD, 2 line, 16 character display. The transmitter's keypad and menu driven display allows the operator to set up the instrument for maximum performance. A RS-232 port is available for remote data link communication. A 4 to 20 mA output signal is standard and the unit is provided with three programmable relays for fault indication. high set point and low set.
The transmitter can be furnished with an optional heater (for ambient temperature below 0°F) and air purge connection.
Dual Range Sensitivity
A key feature of the Model 86 PID is its dual range sensitivity by which the unit can be set to accommodate a broad selection of products on one range and simultaneously provide high sensitivity required for detecting difficult gasoline-to-gasoline interfaces. In the first situation of Figure 3, the zero and span were selected to cover gasoline-to-kerosene interfaces and the second situation represents a high sensitivity range to detect gasoline-to- gasoline interfaces or products with similar or identical API gravities. A separate isolated 4 to 20 mA output is provided for each range.
In Figure 4, the sensitivity of the Model 86 PID is best demonstrated by a comparison to interface detection via densitometry. As shown in the graph, the sound velocity of propane is 750 m/sec at a density of 0.5 SGU; for kerosene it is 1350 m/sec at 0.83 SGU. The respective spans are 600 m/sec vs. 0.33 SGU. The compensated repeatability of the Model 86 PID is 0.25 m/sec. This is equivalent to 1 part in 2400, or in terms of density, 0.33/2400 = 0.00014 SGU. A typical densitometer specification is 1 % of full scale.
Maintenance
The Model 86 PID has no moving parts and is a low maintenance system. The transmitter has self diagnosing electronics and displays alarm conditions. All set up operations are menu driven from the LCD display and entered by the keypad.
Alarms
The Model 86 PID provides high and low alarms that are controlled by keypad entry. There is also a fault alarm to indicate when a problem arises. A Form-C relay is activated by each alarm. The alarm status may be viewed directly on the display or remotely via the RS-232 communication port.
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