Oscar Mayer overcomes temp control challenge; glycol-filled fins gently massage meats; noncontact IR proves most sensible temp control choice.
The plant recently replaced its meat tumblers with upgraded, internally refrigerated vacuum meat massagers. Adding a noncontact infrared (IR) temperature sensor to the control loop of each machine has provided accurate temperature regulation to within a degree.
At Oscar Mayer, whole muscle meats, primarily hams and roast beef products, are combined with spices and curing solutions in sanitary tumblers. Batch sizes range from 7000-8700 lb. (Tumbling brings proteins to the surface to help muscles bond together.) Meats must be processed gently in order to deaerate them. Air pockets can ruin the texture and result in a product that looks less like ham and more like "swiss cheese," according to Bryan McLean, Project Manager.
The previous tumbler worked adequately at lower production speeds, but higher through-put rates produced unwanted elevated temperatures. "Originally we mixed at a slower speed for a longer time to keep temperatures down," said McLean, "but we wanted a way to increase production, so we looked for a way to cool the drum."
McLean and other "Oscar" engineers first tried spraying the drum with chilled water, but a more uniform, controllable system was called for. The solution was a new type of tumbler, a vacuum unit that speeds deaeration and provides gentle handling.
Actually, "tumbler" is a misnomer for this system, which features a double helix configuration of fins inside its chamber. The fins act as flights, passing continuously through the meat mass as the drum rotates to create a gentle meat-on-meat massage. Oscar Mayer ordered its new "massagers" with an optional glycol refrigeration system. To cool the meat during mixing, the system recirculates glycol at 170 F through the drum shaft, through the double helix' fins--which are hollow--and back through the drum shaft.
Mixing, cooling, and automatic self-cleaning cycles are automated by a programmable controller that is accessed via control panel with membrane keypad. Accompanying chart recorders monitor sensor data on drum speeds (typically from 8-12 rpm) as well as glycol and meat temperatures.
IR temp sensing
The heart of all process control is the sensor, and McLean reported having difficulty finding a reliable way to monitor the temperature of meat. This measurement may be taken indirectly by measuring the temperature of the drum, since meat and drum temperatures are identical to within a degree.
According to McLean, "Originally, we had a probe that made contact with a rotary connection. But it never worked right. Frost on the drum would turn to water that ran down onto the probe. After the mixer ran for a while and started to get wet, we couldn't get reliable readings."
McLean's team investigated the sensing alternatives and installed a noncontact IR sensor. The sensor is suspended from the ceiling, four feet above the drum. Its field of view is fixed on a 1.5-inch spot at the center of the stainless steel drum's external surface.
The IR sensing head transmits temperature readings via 4-20 mA output signal to a dedicated signal processing unit. The signal is then passed to a chart recorder and local control panel. If readings rise above 290 F, the glycol pump is activated. Target fin--and meat--temperature are 28[degrees] F. McLean noted satisfaction with the smart sensor's "peak and valley hold" feature, which allows the unit to cancel out or "ignore" specified high and low values. This prevents frost, which covers about 10% of the drum's surface, from skewing the readings.
Through mid-1992, the plant has purchased several more of the glycol units, which now total nine. Based on months of successful testing at Oscar Mayer, the equipment manufacturer has incorporated the noncontact temperature sensors that the Oscar Mayer engineers had helped to "discover."
Additionally, McLean has purchased a portable hand-held IR gun and is having a little troubleshooting "fun" double-checking process temperatures around the plant. Purely for diagnostic reasons, of course.
Vacuum Meat Massagers with Double-Helix[TM] Internal Refrigeration, Challenge-RMF Inc., 17870 Castleton St., Suite 255, Industry, CA 91748.
Model T3 noncontact IR temperature sensor and PM4 hand-held IR gun, Raytek, Inc., 1201 Shaffer Rd., P.O. Box 1820, Santa Cruz, CA 95061-1820.
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|Date:||Dec 1, 1992|
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