Measuring Liquids in the Food Production Industry with Transmitters and Transducers

Ultrasonic sensors transmit sound waves that range above the range of human hearing, (more than 20 kHz). These sound waves echo off the surface of a set target, the waves repel off the target (i.e. the base of a vessel holding pulp and juice) and return to an ultrasonic level transmitter to record flow and level monitoring equipment.

Ultrasonic level transmitters are used to monitor flow and level of liquids in the food production sector. Procedures for Safety Integrity Level (SIL) and instrumentation are designed for reliability in testing and certification in accordance to regulation in liquid manufacture and food production industries.

Food science has accepted the value of using ultrasonic waves for safe and accurate measurement and monitoring when sensory systems are required for detection and precision monitoring of liquid levels.

Measuring Liquids in the Food Production Industry

How Ultrasonic Level Transmitters Work

Continuous ultrasonic pulses track levels in vessels while mounted at the top of the tank above the blocking distance. Pulses move through the empty distance of the vessel, above the fluid surface in the tank, traveling through the fluid (pulp, juice, or other aqueous fluids) to the bottom of the tank. The ultrasonic sensor and the detection target at the bottom of the tank measure the travel distance from the liquid level to the bottom of the tank.

The calculation of the time it takes for the ultrasound pulse signal to travel from the ultrasonic transmitter to the target and back relies on the accurate standard of the speed of sound in the air environment. Dividing the pulse travel time by two, and multiplying the result by the speed of sound, offers the precise level of juice in the vessel.

Non-contact level transmitter

Non-contact level transmitter


    Level = particular airspeed of sound in manufacturing environment X time delay ÷ 2.

Hazard Analysis and Critical Control Points (HACCP)

The Food and Drug Administration (FDA) Principles Application Guidelines regulates Food Manufacturers. During manufacturing and food production of colloidal fluids, monitoring of crucial limits of each control point to prevent, limit or lessen safety hazards to a suitable level, fall under the Title 21 Code of Federal Regulations (CFR) Part 120.1(a). Proof testing is a vital part of confirming the safety function of a level instrument.

Level Instruments such as ultrasonic level transmitters, switches, flush mount pressure transducers, RF level transmitters and other SIL instrumentation are systems that are present to prevent and regulate the possibility of risky events. This equipment is certified to detect an overfill condition in a tank or vessel. End user testing processes, such as proof level or partial proof testing of level instruments, to maintain SIL ratings prevent failures of instruments or the overflowing of tanks, maintaining suitable safety levels.

The IEC 61508 standard offers a systematic approach for the design and testing of products in safety-related applications. The International Electro-technical Commission (IEC) defines Safety Instrumented System (SIS) and compiled the standards. IEC 61508 defines level instrument requirements compliance, which applies to food production manufacturers and suppliers of SIL products.

Measuring a Single Discreet Liquid Height

Point level measurement sensors indicate a pre-set liquid level condition in the pulp or juice manufacturing process. These sensors track over-fill conditions, activating a high alarm function.

More advanced continuous level sensors offer level monitoring of whole systems. Instead of just monitoring a critical point in the juice production process, level interface detection sensors measure liquid levels within a precisely set range.

Analog output directly relates with pulp or juice levels in vessels or tanks. The system can be linked to a visual indicator and a process control loop that creates the full level monitoring management system.

Measuring the Level with a Pressure Transducer

The level of the liquid can be calculated using a pressure transducer and the following equation.

    p = h ρ g (1) (N/m2, Pa, lbf/ft2, psf)

p = pressure or ρ = density of liquid (kg/m3, slugs/ft3)
h = height of the fluid column, or depth in the fluid at which the pressure is measured (m, in)
g = the gravitational, (acceleration), constant (9.81 m/s2, 32.17405 ft/s2)

The Advantage of OMEGA® Transmitters and Transducers in Juice Production, Food Production and Liquid Manufacturing

If an operation requires a micro-machined, silicon sensor built to provide a highly stable transducer with remarkably high accuracy, ideal for pressure or level applications, the OMEGA® PX409S-USBH sanitary series offers long-term stability. OMEGA’s 3A approved sanitary series connects straight to the PC or enterprise setup. It is provided along with standard USB cable termination for easy installation and accurately logging data and speedily charting the readings.

The fitting pressure transducer is ruggedized with a secondary containment system, gage and absolute pressure to 600 psi. The pressure transducer is installed inside the bottom of the vessel. The compound gage provides ±10 in H2O to ±15 psi. The sealed gage 100 to 600 psi, vacuum 10 in H2O to 15 psi, and barometric ranges include 32 in Hg or 1100 Torr.

PX4095S-USBH series

PX4095S-USBH series

The installation and operational software is provided free of cost. In case users want to use the PX409S-USBH, they should ensure the inside the vessel is the same pressure as the outside. If there is a differential of pressure inside the vessel, it is recommended to use a differential pressure transducer. When the juice product, or another fluid, contains flesh or pulp, the use of a flushed pressure transducer is compulsory. Otherwise, the pulp will hinder this transducer.

In fact, OMEGA is a one-stop source for all process measurement and control parts and system devices. Pressure transducers can be added for high-performance thin-filmed pressure transducer specifications, fundamentally safe pressure transmitters and advanced silicon technology to micro-machined silicon transducers with wet/wet differential pressure. If operation requirement specifications reach beyond OMEGA’s standard models, they offer custom designs engineered for general purposes, hazardous locations, flush diaphragms, heavy-duty industrial - high accuracy and those specific to PC board mountable solutions.

Capacitive (RF) point level switches

Capacitive (RF) point level switches

Whether your food production or other manufacturing concerns is level consistency, submersible, sanitary or for any specific purpose, OMEGA’s Design Engineers can meet the challenges. OMEGA’s capacitated (RF) point level switches series LVCN6000/7000 are perfect for low and high-level detection monitoring of both liquids and solids.

This information has been sourced, reviewed and adapted from materials provided by OMEGA Engineering Ltd.

For more information on this source, please visit OMEGA Engineering Ltd.


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