To monitor the pulse of a food, beverage, or dairy plant, measurement instrumentation is used. These devices ensure that process temperatures, levels, pressures and flows are operating on specification correctly. When transmitters are not correctly chosen, spare parts inventories swell, tanks overflow, instruments break, and so productions lines could stop.
Dairies, as well as food and beverage facilities, are challenging environments with a number of corrosive liquids and materials. Furthermore, hygienic and sanitary operating conditions are critical to stop product contamination and spoilage. These issues place increased importance on process measurement selection and installation.
Experience indicates that there are five major issues that inhibit measurement performance. These “hidden dangers” are easily managed and, if avoided, can significantly enhance your operations.
Number 1: Susceptibility to Diaphragm Damage
The flush diaphragm in a measurement instrument is a fragile, yet critical part. It is an extremely thin element which is highly vulnerable to damage when used in a challenging production environment.
Diaphragms are typically damaged in one of several ways:
- Overpressure from cleaning or process fluids can put too much force on the diaphragm, resulting in a bent component.
- Even pressure from a fingernail can cause damage. During handling and installation, the instrument is struck, dropped, or improperly inserted in a connection, causing damage.
- Nozzles used in tank or process cleaning can impact the instrument, impairing a delicate diaphragm element.
A damaged diaphragm causes instrument inaccuracy that can disrupt the production process.
In an empty tank, for example, the level transmitter should give an output of 4 milliamps. If the diaphragm has been damaged, it may show 5 milliamps — a 7% error that mistakenly indicates that there is fluid in the tank.
Some measurement transmitters incorporate ceramic diaphragms; these components are particularly susceptible to damage from overpressure. Furthermore, they are vulnerable to temperature shocks and thermal effects that can consequently cause devices to display inaccurate data. To seal the ceramic sensor in the transmitter, ceramic diaphragms also require O-rings.
O-rings add to maintenance costs, as they can wear out from exposure to acids and corrosive fluids. Invest in devices that possess smaller, thicker stainless-steel diaphragms which are flush with the process when evaluating process measurement instruments. The instrument’s wave structure should be mounted directly behind the diaphragm and be equal in size.
This construction is much less susceptible to damage, as it provides protection against overpressure and mishandling. Additionally, not every transmitter is repairable. Seek out instruments that can be refurbished with replaceable components.
Number 2: Inferior Instrument Housings
A measurement instrument’s housing has to protect its internal components from an extremely unfriendly environment. Wide temperature variations, caustic wash-down solutions, and rough handling can significantly affect measurement performance. Various transmitters are protected by aluminum housings that may not endure the rigors of beverage and food processing environments.
The top measurement devices include polished 316 stainless-steel housings and connections. Their extremely smooth surfaces adhere to 3A sanitary standards and give much better clean-in-place (CIP) and sterilize-in-place (SIP) performance.
Shorter cycle times with less water and materials costs result in easy cleaning and hygiene. Furthermore, the ruggedness of the stainless steel is also more successful in protecting the instrument’s internal components
Number 3: Incompatible Instrument Connections
If you visit a brewery or dairy, you will observe measurement instrumentation from a variety of manufacturers. A number of supplier’s products use different electronics, calibration methodologies, process connections, and programming points.
Swapping one instrument brand with a different one can mean cutting the original device out of a tank or pipe and then re-welding new weld spuds, which is an expensive and time-consuming process, and there will be new maintenance and calibration procedures to learn.
A facility can replace all of its measurement devices with a single brand which can easily plug and play in their process, since at least one manufacturer’s instruments are compatible with any variety of process connection.
Additionally, an individual faulty instrument can be swiftly replaced with no need for welding or retrofit work, minimizing process downtime. This ability also benefits from standardized electronics, calibration, and programming over its range of measurement infrastructure.
Number 4: Inadequate Temperature Compensation
As part of their daily operations, food and beverage processes usually experience wide temperature variations. For example, pipes and tanks that hold cold milk can be put through clean-in-place solutions of up to 194 °F.
These fast temperature changes can trick measurement sensors that do not have good temperature compensation, resulting in incorrect process readings. These incorrect readings can cause manufacturing cycles to start or stop at the wrong time, balance tanks to overflow, or automatic cleaning cycles to malfunction.
Production lines can be severely interrupted by these measurement inaccuracies; product is spilled on the floor and lost. Materials drain into effluent causing environmental issues. The equipment must be halted, cleaned, repaired, and then restarted. All of these issues cost time, money and lost production.
Deficient temperature compensation typically occurs for two reasons:
- The instrument’s sensor is located too far away from the process to measure the changing temperature rapidly and accurately.
- The oil reservoir between the instrument’s flush diaphragm and sensor is too large and takes too long to react to the changing temperature. This creates a signal drift due to hot/cold operations.
These issues will result in imprecise instrument readings when wide or quick process temperature fluctuations occur. When assessing measurement technologies, instruments that employ active temperature compensation technology are best. These devices only have a small space between the diaphragm and the sensor, with ¼ inch being the optimum distance.
They also possess small oil reservoirs that can react and compensate quickly to temperature adjustments. The lower the quantity of oil, the less variability will be seen in the measurement. Instruments which offer these characteristics will achieve 0.1% accuracy against 0.25% to 0.5% for those which do not. Active temperature compensation is a crucial element in minimizing maintenance costs and downtime.
Number 5: Full-Scale Versus Adjusted-Span Measurement
Manufacturers’ accuracy ratings are all different. Some manufacturers measure their devices’ accuracy on a “full-scale” basis (its maximum span value). Yet, if your application utilizes a smaller span, the instrument will not be as precise.
Transmitters that measure their accuracy on an “adjusted-span” basis should be employed. This ensures that the device’s accuracy will be the same at any point in its calibrated span range. 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%.
If the transmitter is rated on a full-scale (or full-scale-output) basis, however, then it will generate 0.1% accuracy at 10 psi, but will be 10 times less precise at the application’s 1 psi. It is also a good idea to choose transmitters that incorporate adjusted-span accuracy ratings with large span ranges. These devices can be calibrated effectively across a very wide range of applications.
For example, an instrument with 0.1% precision on an adjusted-span basis, with a span range of 47 inches to 470 inches, can be used across a large range of silo sizes whilst maintaining its accuracy.
As a result, food and beverage manufacturers can utilize the same instrument for most of their silos and tanks and without affecting accuracy. This means fewer spares are required to be kept in inventory, whilst guaranteeing precise process measurement.
Process measurement is a crucial aid to food and beverage plant performance. Downtime and maintenance costs can be impacted significantly by instrument choices.
For best practice:
- Ensure instruments have stainless steel housings for easy cleaning and good hygiene
- Look for instruments with limited oil reservoirs and integrated sensors that provide active temperature compensation
- 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
- Seek transmitters with flexible process connections to reduce installation time and costs
- Place a high value on instruments that can be refurbished with replaceable components
Avoiding the hidden dangers of process measurement will help keep your beverage or food facility working profitably and smoothly.
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.