Selecting Meters for Your Food
or Beverage Processing Facility
To be effective, a monitoring & targeting (M&T) system
must meet your strategic objectives for cost control, be designed
to be compatible with your processing flows, and incorporate hardware
(and software) to measure and collate data into a useable form.
The purchase, installation and commissioning of a monitoring and
data management system requires an investment of both time and capital.
Getting started
A complete monitoring and data management system should include:
- Flowmeters to monitor gas, electricity, steam, compressed air
or any other energy stream;
- Transducers and transmitters linked to flowmeters to record
and send the data to a receiving location;
- A data logger to store and sort the data;
- A method to transmit the data to a computer system to be entered
in an electronic data management package.
There are many kinds of flowmeters available, each with specific
applications. Most meters also require "add-ons" to accommodate
different pipe configurations. Although the choice of meter can
be relatively straightforward, installation can be complex.
Application and installation considerations
Practical considerations affect where a meter can be placed within
a given location. Disturbances upstream (and sometimes downstream)
of a flowmeter (like pipe elbows and control valves) affect a meter's
accuracy. It is important to ensure that valves are located downstream
of a flowmeter. The pipes upstream and downstream of a flowmeter
need to be long enough to create a laminar flow and remove the disturbances
that affect measurement accuracy. In some cases, a section of straight
pipe 10 to 50 pipe-diameters in length is required upstream of the
meter. A device called a flow straightener can solve this kind of
challenge.
It's important to choose the right meter to address installation
constraints. Most technologies have many applications, but will
fail to perform in certain configurations. Only certain flowmeters
may work in your plant. Keeping your application in mind, select
the desired meter based on accuracy, cost, durability, and reliability.
Tip: Most meters must be installed by a licensed technician.
Choosing a meter
A number of meters are good choices for food processing applications.
The most common choices are summarized below:
Thermal mass flowmeters (for gases)
Thermal mass flowmeters use the thermal properties of a gas to
measure flow. The detector has two sensors - one to measure the
amount of heat applied to it (this heat dissipates into the gas
in proportion to the flow) and the second to measure the temperature
of the gas (which measures the amount of heat lost by the gas).
An electronic transmitter uses heat input and temperature loss to
determine flow. The cost of a thermal mass flowmeter, most commonly
used to measure natural gas flows, typically starts at $5,000 for
a 2-inch-diameter pipe.
Advantages:
- Fast response and can measure low flows
- No moving parts
- Easy to install but may need flow conditioning
Disadvantages:
- Can only be used for clean gases (e.g., natural gas)
- Not suitable for gas streams with fluctuating heat load
- Streams must be "dry," not "wet" gas
Vortex flowmeters (for fluids and gases)
Vortex meters are good for monitoring fluids and gases like compressed
air, steam, boiler feed water, and other clean gases or liquids.
The technology uses an engineered obstruction in the middle of the
stream to generate a downstream vortex. As flow increases oscillation
frequency, a sensor detects the oscillations and an electronic transmitter
generates a flow signal. Typical costs increase with pipe diameter.
For example, a 3-inch-diameter pipe is $4,000, a 6-inch diameter
is $7,500, and an 8-inch diameter is $9,000.
Advantages:
- Can measure energy utilities, such as steam, hot water, condensate,
compressed air, etc. independent of temperature
- Accurate and easy to install; however, a flow conditioner is
often required
Disadvantages:
- Turns off at low flow, so applications must be in correct flow
range
- Sympathetic pipe vibrations can affect readings
Magnetic flowmeters
A magnetic flowmeter measure the velocity of a conductive liquid,
such as water, acids, caustic and slurries. It works by creating
a magnetic field with voltage and sensors on the pipe walls. As
the liquid moves faster, more voltage is generated in proportion
to the flow. An electronic transmitter processes the voltage signal
to determine liquid flow. This flowmeter does not obstruct flow
and can be applied to many liquid streams, including clean, dirty,
corrosive or abrasive streams. It is commonly used on process water
and wastewater streams. Costs are similar to vortex meters (see
above).
Advantages:
- Highly accurate and does not create a pressure drop
- Can monitor a variety of clean and dirty liquids
Disadvantages:
- Not suitable for liquids with low conductivity (i.e., deionized
water, boiler feed water)
- Electrodes subject to coating and require regular maintenance
Electrical meters
Solid-state meters with LCD display or automatic-reading functions
can replace older electromechanical meters. They can record load
parameters like demand, power factor and reactive power. By adding
an electronic clock mechanism, this meter can provide "real-time"
or time-of-day use, which is critical for peak electricity demand
management. Costs for electrical meters can range from $500 to $50,000,
depending on the size and complexity of the load being managed.
From installation to implementation
Installing a meter is only the first step. Data retrieval and management
is an equally important function. A meter's signal is usually sent
to a data logger, which converts the signal to useable data. The
data is stored in internal memory to download later to a computer.
Although there is a lot of choice in the marketplace, the key components
include:
- Hardware to digitize the signal and convert it to meaningful
units or data;
- Internal memory and data storage capabilities (the required
amount of internal storage can be calculated based on sample or
polling rates from the sensors); and
- Data logging software for data acquisition, analysis, and presentation
(many manufacturers provide generic software with the logger to
sort and manage the data).
Data from the logger can be transferred to a computer for long-term
storage and management. This can be done manually, using a microchip
or by connecting the computer to the logger. The best option, however,
is to use a modem or wireless technology to transfer the data to
a computer or server. A good data logger can cost around $4,000
but the installation and transmission/distribution of the signal
will be extra and will depend on distances, automatic data transfer,
etc.
Metering systems can generate large amounts of data. Software is
important to translate and analyze the information in order to assess
progress in relation to objectives and targets, and to draw conclusions.
Software options include commercially available packages, software
that comes with the data logger or Excel spreadsheets that you have
developed internally. In all cases, the application can include
imbedded calculations and graphics that help analyze the data with
the click of a mouse.
Software packages designed to manage the data vary widely in cost
and are completely dependant on your objectives. Some users are
able to integrate the free generic software packages that may come
with a data logger. More sophisticated packages develop tailored
reports specific to your objectives and can cost between $5,000
and $15,000. Highly complex and transnational facilities may need
to invest tens of thousands of dollars for a software package that
integrates data from their global operations.
The time you invest in designing the hardware components of your
M&T program will help you achieve your strategic objectives.
In summary, a successful system will result from:
- Choosing technically sound meter locations (may require expert
advice);
- Having a licensed technician install the meters;
- Ensuring data collection and storage are as automatic as budgets
allow;
- Customizing data management to meet your objectives (potentially
using readily available spread-sheet programs, such as Excel).
Additional resources
OMAFRA fact sheets:
Companies that specialize in installing M&T systems include:
