Monitoring the level of liquid can be accomplished through the use of a pressure transducer. The density of the liquid and its height create pressure on the diaphragm of the pressure transducer to generate an accurate and cost-effective level measurement. Generally, pressure transducers can be used for level measurement from 10 inches of water column up to 10,000 PSI (700 bar).

Designed with stainless steel and Hytrel materials, submersible pressure transducers are reliable, cost-effective instruments to measure the level of various liquids including water and diesel. These pressure sensors are an ideal choice for mobile applications such as ships, train cars, or when the tank is transported between locations such as for construction sites, chemical totes for industrial processing, or well site injection chemicals.

A variety of factors should be considered when installing a submersible pressure transducer in a tank. The figure shows one installation method used by American Sensor Technologies for its AST4510 submersible transducer using a rigid pipe. The transducer comes standard with a 1/2" NPT male conduit connection at the base of the cable connection. In tanks that are turbulent due to an inlet/fill pipe or the use of an agitator, the transducer can have rigid plastic or metal conduit installed over the cable to prevent sensor movement within the tank.

The conduit over the cable is mounted to a bung at the top of the tank. Parts that thread onto a 1.5" female NPT bung and have a 1/2" female NPT thread can mate the ridid conduit. The cable exits the tank and is held in place by a cord grip that runs to the control box. The same cable grip can be used at the junction box, ensuring that the vent tube is clear. Depending on hazardous location requirements, this can be in the non-hazardous area with connection to the intrinsically safe barrier. In this example, it is expected that the junction box is properly vented to the atmosphere to prevent water ingress.

In this application, the pressure sensor was installed above the base of the bottom of the tank. As sludge and silt tend to line the bottom of the tank, a height of 100 millimeters was calculated to ensure the process connection did not clog over time. The diaphragm of the transducer is close to the top of the process connection hex, so operators can calculate the offset from when the tank is empty.

Other applications may have the submersible pressure transducer installed directly into an intrinsically safe radio device at the top of the tank. This reduces the cost of the transducer, as less cable and less time are required for the installation. With shorter cable lengths, a voltage output signal with low current consumption is an option if the system is battery operated. Less current consumption means longer battery life and less maintenance.

This article was contributed by American Sensor Technologies (AST), Mount Olive, NJ. For more information, Click Here .

Motion Control & Automation Technology Magazine

This article first appeared in the June, 2014 issue of Motion Control & Automation Technology Magazine.

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