Seri Palm Oil Case: Edible Oil and Syrup Tank Level Measurement With Rod-Antenna 80 GHz Radar

In a food plant, the cleaning cycle is part of the measurement problem. This article is organized around a specification lesson from a food processing plant: level instruments on edible oil and sugar syrup storage tanks must survive the CIP cycle before they are allowed to measure anything. The media are vegetable oil (dielectric constant approximately 3) and syrup, in stainless steel tanks cleaned with hot caustic, water and steam. The previous differential pressure transmitters drifted because their readings depend on density, which changes between products; ultrasonic devices failed in steam and foam. The replacement - an 80 GHz FMCW radar with a rod antenna for low-dielectric media and a hygienic process connection - measures the surface directly, so density drops out of the equation, and its materials and design tolerate the CIP environment. The article explains the specification decisions in the order a buyer actually meets them.

Client Profile: Seri Palm Oil Processing Sdn. Bhd. (Malaysia)

Seri Palm Oil Processing Sdn. Bhd. is a palm oil refining and fractionation plant in Malaysia operating edible oil and syrup storage tanks that feed the batch kitchen. The tanks are cleaned in place with hot caustic and steam, so the level instruments must survive the CIP cycle and return to accurate measurement immediately after - while handling the weak radar echo of low-dielectric edible oil.

2. The Tanks: Oil and Syrup in the Same Building

The plant stores vegetable oil and sugar syrup in vertical stainless steel tanks that serve the batch kitchen. Oil is kept warm enough to pump; syrup is stored at ambient and batched by recipe. Every tank is cleaned in place: hot caustic solution, water rinses, and a steam phase, delivered through CIP spray balls. The instrument on each tank therefore lives through a cycle that most level sensors never survive - and it must return to accurate measurement immediately after, because batching starts as soon as the tank is declared clean. Any specification that ignores the CIP cycle fails in the first month, no matter how good the measurement is in a clean tank.

3. Two Media, Two Physics Problems

Vegetable oil has a dielectric constant of approximately 3, so it reflects only a small fraction of a radar wave - the echo is weak, and only the right frequency and antenna design will see it at all. Syrup has a higher dielectric constant but a density that changes with concentration and temperature. The two media expose the two classic failure modes of level measurement: weak echoes from low-dielectric liquids, and density-dependent readings from hydrostatic methods. Any solution had to handle both - and then survive the CIP cycle on top.

4. Why the Pressure Transmitters Drifted

The differential pressure transmitters measured level from hydrostatic head: pressure divided by density. The method is only correct while the density is constant and known. In this plant it was neither - oil and syrup have different densities, and syrup density changes with concentration and temperature - so the same liquid height produced different readings at different times. Inventory reconciliations failed and batches were dosed from a level that was not what the tank contained. The impulse lines added a second problem: they needed maintenance and could clog with syrup. Ultrasonic devices tried in some tanks failed differently: the steam phase of CIP attenuated the pulse completely, and filling foam produced jumps. Neither technology answered the real requirement: measure the surface directly, independent of density, through steam and foam.

5. The Hidden Specification: Surviving the CIP Cycle

The CIP cycle is the specification that filters out most instruments, and it should be written into the tender before anything else. The instrument must withstand hot caustic at close range from the spray balls, steam at its housing and cable entry, and thermal cycling - then measure accurately within minutes of the cycle ending. This drove three decisions. First, a crevice-free hygienic process connection (sanitary clamp or flange) in food-contact-approved material, so the instrument is cleaned together with the tank instead of being removed. Second, an antenna material that tolerates caustic and steam - PTFE or a coated face. Third, a housing rated for the washdown environment (IP66/IP67). These are not accessories; they are the difference between an instrument that lasts years and one that fails at the first CIP. The hygienic connection must be crevice-free for a physical reason: a crevice harbors product and bacteria and sits unreachable by the CIP spray, which is why the connection geometry is part of the food-safety specification, not a cosmetic detail.

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7. The Rod Antenna and the Low-Dielectric Echo

With the CIP requirement settled, the measurement design could proceed. An 80 GHz FMCW radar was chosen, with a rod antenna optimized for low-dielectric media. The reasoning: the 80 GHz band concentrates more energy in a narrower beam, which helps return a usable echo from oil; the rod acts as a short waveguide that concentrates the radiated energy along the antenna axis, raising the echo from a low-dielectric surface. Steam is not a problem for microwaves the way it is for ultrasound - the signal passes through steam and light condensate, so the post-CIP atmosphere does not blind the instrument. The same transmitter measures syrup without reconfiguration, because syrup's higher dielectric constant only makes the echo stronger.

8. The Configuration Sheet

The configuration was deliberately minimal. Tank height and mounting offset entered; output scaled 4-20 mA over the working range; HART enabled for remote diagnostics. The echo threshold was set for low-dielectric media on the oil tanks, so the weak oil echo was detected reliably; the standard threshold sufficed for syrup. Damping was set to a few seconds to smooth filling turbulence and foam-induced noise. The fail-safe direction was set so that a lost echo - for example during the steam phase of CIP - drives the output to a defined state the PLC treats as 'measurement unavailable' rather than as a real level. That single setting prevents the batch kitchen from dosing on false data after a cleaning cycle.

9. Installing Hygienically

Installation respected both the measurement and the hygiene program. The radar was top-mounted on the sanitary connection with the rod below the nozzle into the tank, positioned away from the CIP spray ball's direct spray path where possible - a small detail that extends antenna life by keeping caustic blast off the face. The rod length was checked to reach below the nozzle but stay clear of the bottom outlet and any agitator. The instrument was mounted vertically; a tilted antenna changes the measured distance. The hygienic gasket was food-grade and scheduled for replacement with the tank's other gaskets. The cable ran in conduit with a drip loop so condensate could not enter the housing.

10. Commissioning With a Live CIP Run

Commissioning covered both the measurement and the cleaning cycle, because both are part of the duty. The empty-spectrum and false-echo map were recorded with the tank empty and clean; the level output was verified against a dip or weighed batches at two or three levels - on oil, agreement within approximately +/-5 mm is expected depending on surface condition. Then the CIP cycle was run with the instrument live. The echo curve was watched during the steam phase: the transmitter should report the defined 'measurement unavailable' state, not a false level, and recover cleanly when the steam clears. The echo threshold and damping were adjusted if the steam phase produced marginal echoes. Finally, the batch PLC integration was tested end to end - level values, diagnostics and alarm states all reaching the control system correctly.

Why Choose Qinwei Instruments

Xi'an Qinwei Instrument Factory (brand QINWEIYB) is a manufacturer established in 2010 that specializes in industrial automation instruments, with 500-800 employees and 50%-60% of output exported worldwide. For food-grade service, Qinwei offers rod-antenna radars optimized for low-dielectric media, sanitary process connections and crevice-free designs that tolerate CIP caustic and steam. All instruments are factory-calibrated with traceable certificates; MOQ starts from 1 set, delivery is 5-8 working days, and OEM/ODM customization is supported.

12. What the Batch Kitchen Saw

After commissioning, the change appeared first in the reconciliation sheet. The same tank now measures oil and syrup without re-ranging, because the measurement is geometric, not hydrostatic - density dropped out of the equation. The steam phase of CIP no longer produced false readings; the instrument reported the unavailable state and recovered cleanly. Foam during filling no longer caused batching errors. Inventory could be reconciled with weighed deliveries - something the density-dependent DP installation could not do consistently. Site-specific reconciliation figures are not provided; the design removed the three error sources - density, steam and foam - so the cleaning cycle no longer interrupts trustworthy measurement.

13. Engineering Value, and the Applications That Follow

The value chain in a food plant is direct: density independence removes batching errors and protects recipe consistency; CIP tolerance removes the labor of removing, drying and reinstalling instruments; hygienic design keeps the plant compliant in audits; and the weak-echo design means the harder case (oil) is measured as reliably as the easy one (syrup). The same configuration applies to edible and essential oils, syrups, molasses, juices and other liquid foodstuffs in storage and batching tanks, and to any tank where CIP steam defeats ultrasonic devices. For very viscous or sticky media that coat antennas, verify self-cleaning behavior before installation; where tanks hold alcohol or solvents in classified areas, specify the Ex-rated version of the same radar. When requesting a quotation for food-grade level measurement, provide the product and its typical temperature, tank height and connection size, whether CIP with steam is used, and the sanitary standard required for the process connection.