Measurement instrumentation is used to monitor the pulse of a beverage, food, or dairy plant. Devices such as these make sure that process temperatures, flows, pressures, and levels are operating properly and on specification. If transmitters are not chosen properly, instruments break, tanks overflow, spare parts inventories swell, and productions lines may stop.
Food and beverage dairies and facilities are challenging environments, with numerous corrosive substances. Additionally, hygienic and sanitary operating conditions are especially crucial in such industries to avoid spoilage and product contamination.
These concerns add importance to process measurement selection and installation. There are five major issues that impede measurement performance. These “hidden dangers” are easily managed and can significantly enhance your operations if avoided.
Number 1: Inferior Instrument Housings
The job of a measurement instrument’s housing is to shield its internal components from a very unfriendly environment. Caustic wash-down solutions, rough handling, and wide temperature variations, can impact measurement performance significantly. Numerous transmitters are protected by aluminum housings that may not be able to withstand the rigors of the food and beverage processing environment.
The optimum measurement devices come with polished 316 stainless-steel connections and housings. Their exceptionally smooth surfaces provide much better clean-in-place (CIP) and sterilize-in-place (SIP) performance and meet 3A sanitary standards. Easy cleaning and hygiene result in shorter cycle times with lower water and materials costs. The ruggedness of the stainless steel is also more effective in shielding the internal components of the instrument.
Number 2: Susceptibility to Diaphragm Damage
A critical, but fragile component in a measurement instrument is the flush diaphragm. It is a very thin element which is highly susceptible to damage in a challenging production environment.
Diaphragms typically suffer damage in a number of ways:
- Overpressure from cleaning or process fluids can put too much force on the diaphragm, resulting in a bent component.
- Nozzles used in tank or process cleaning can impact the instrument, impairing a delicate diaphragm element.
- During handling and installation, the instrument is dropped, struck, or improperly inserted in a connection. Even pressure from a fingernail can result in damage.
The production process can be disrupted by a damaged diaphragm, which causes instrument inaccuracy.
In an empty tank, the level transmitter should provide an output of 4 milliamps. However, if the diaphragm has been harmed, it could indicate 5 milliamps — a 7% error that wrongly shows that there is fluid present in the tank.
Many measurement transmitters include ceramic diaphragms. These components are extremely susceptible to harm from overpressure. Additionally, they are susceptible to temperature shocks and thermal effects which can result in device inaccuracy. Ceramic diaphragms also need O-rings in order to seal the ceramic sensor in the transmitter.
O-rings can wear out from exposure to corrosive fluids and acids, which adds to maintenance costs. The instrument’s wave structure should be mounted directly behind the diaphragm and be equal in size. When assessing process measurement instruments, invest in devices that have smaller, thicker stainless-steel diaphragms that are flush with the process.
This construction gives protection against mishandling and overpressure and is much less susceptible to damage. As not all transmitters are repairable, instruments that can be refurbished with replaceable components should also be considered.
Number 3: Inadequate Temperature Compensation
Food and beverage processes typically experience large variations of temperature as part of their daily operations. As an example, tanks and pipes that hold cold milk can be subjected to clean-in-place solutions of up to 194 °F.
These quick temperature swings can confuse measurement sensors which do not have good temperature compensation. This results in inaccurate process readings that can cause automatic cleaning cycles to malfunction, balance tanks to overflow, or manufacturing cycles to start or stop at the wrong time.
These measurement inaccuracies can therefore cause havoc on production lines. If a spillage occurs, product is lost and equipment must be stopped, cleaned, repaired, and restarted. Materials can drain into effluent which causes environmental issues. All of this costs lost production, time, and money.
Deficient temperature compensation normally occurs for one of two reasons:
- The oil reservoir between the instrument’s sensor and flush diaphragm is too big, and so takes too much time to react to the changing temperature. Due to hot/cold operations, this creates a signal drift.
- The instrument’s sensor is placed too far away from the process to measure the changing temperature accurately and quickly.
These issues will lead to inaccurate instrument readings when wide or rapid process temperature changes happen. Aim to purchase instruments that employ active temperature compensation technology when evaluating measurement technologies. Such devices have minimum space between the diaphragm and the sensor, with ¼ inch representing the ideal option.
They also have small oil reservoirs which can react and rapidly compensate for changing temperatures. The lower the quantity of oil, the less variability will be seen in the measurement. Instruments which have these characteristics will perform at 0.1% accuracy, against 0.25% to 0.5% for those which do not. Active temperature compensation is a key component for minimizing downtime and maintenance costs.
Number 4: Full-Scale Versus Adjusted-Span Measurement
Manufacturers’ accuracy ratings are not necessarily equivalent to one another. Some calculate their devices’ accuracy on a “full-scale” basis (its maximum span value), but the instrument will not be as accurate if your application uses a smaller span.
It is crucial to find transmitters that measure their accuracy on an “adjusted-span” basis. This means, at any point in its calibrated span range, the accuracy of the device will be the same. For example, an instrument is rated for a minimum span of 1 psi and a maximum span of 10 psi. The transmitter is calibrated for an application of 1 psi. If the instrument’s accuracy rating is measured on an adjusted-span basis, then the accuracy at 1 psi will be 0.1%.
However, if a transmitter is rated using a full-scale (or full-scale-output) basis then it will have 0.1% accuracy at 10 psi but it will be 10 times less accurate at the application’s 1 psi. It is also worthwhile to select transmitters that combine wide span ranges with adjusted-span accuracy ratings.
These devices can be effectively calibrated across a very wide range of applications. An instrument with 0.1% accuracy on an adjusted-span basis with a span range of 47 inches to 470 inches can be employed over a wide range of silo sizes whilst maintaining its accuracy.
That means that, without compromising accuracy, food and beverage manufacturers can use one instrument for most of their tanks and silos. The result is fewer spares in inventory, while confirming precise process measurement.
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Number 5: Incompatible Instrument Connections
When looking around a dairy or brewery, you will often see process measurement instrumentation from a number of manufacturers. Many suppliers’ products utilize different calibration methodologies, process connections, electronics, and programming points.
Replacing one instrument brand with another can be a time consuming and expensive process, which can involve cutting the original device out of a tank or pipe, and then re-welding new weld spuds. There are also new maintenance and calibration procedures to learn.
At least one manufacturer’s instruments are compatible with any kind of process connection, which means a facility can replace all of its measurement devices with one brand that will plug and play in their process easily.
Furthermore, in this way, a single faulty instrument can be replaced quickly, without the requirement for welding or retrofit work, minimizing process downtime. The facility also benefits from standardized electronics, programming, and calibration across its measurement infrastructure.
Conclusion
Process measurement is a huge factor in food and beverage plant performance. Instrument choices can make a significant impact on maintenance cost and production downtime.
To ensure best practice:
- Make sure devices are rated for adjusted-span measurement for high accuracy across the entire span range.
- Explore devices that offer small, thick stainless-steel diaphragms that resist damage.
- Look for instruments with limited oil reservoirs and integrated sensors that provide active temperature compensation.
- Ensure instruments have stainless steel housings for easy cleaning and hygiene.
- Seek transmitters with flexible process connections to reduce installation time and costs.
Additionally, place a high value on instruments which can be refurbished with replaceable components and avoid the hidden dangers of process measurement to help keep your food or beverage facility running smoothly and profitably.
This information has been sourced, reviewed and adapted from materials provided by Klay Instruments B.V.
For more information on this source, please visit Klay Instruments B.V.