Flow Totalization in Gas Usage Monitoring

October 31st, 2016 No comments

A common application where accurate flow totalization is required is gas usage monitoring. In this application there is typically a single source of gas being shared by several different users or locations within a facility. To account for usage, or allocate costs properly, the facility needs to monitor the amount of gas consumed by each user.

Typical Installation

A typical installation for this application includes several flow meters, secondary electronics with totalizer function cabling from each device connected to a central monitoring system. The totalizer gets a flow signal from the flow meter, calculates the totalized flow and sends that value to the central monitoring system.

Gas Usage Monitoring Diagram

Typical gas usage monitoring installation

With this approach the accuracy of the totalized flow may not be optimized. There may be some additional error due to resolution of the analog to digital converters (ADC) and signal noise. The user also needs to be sure the analog signals were calibrated properly and that they match the span and time units of the flow meters. Signal filtering, signal cutoffs, sample rates and sample period can also have an impact. All of these factors could lead to improper billing or cost allocation. There is also additional hardware and cabling costs with this approach that could be avoided.

A Lower Cost Approach

An alternate approach uses digital mass flow meters, like the Brooks SLA Series, which calculate the totalized flow value internally. With this approach, no additional inaccuracy is introduced with a secondary calculation or digital to analog conversion.

Gas Usage Monitoring Diagram Using Brooks SLA Series MFCs

Gas usage monitoring installation using Brooks SLA Series Mass Flow Meters

 

 

 

 

 

 

 

 

 

Another advantage of this approach is that the user is able feed the totalized flow value directly to the gas monitoring system via digital communication. This eliminates the need for the totalizers and simplifies the wiring, therefore reducing the total installed cost of the system.

Validating Totalized Flow Accuracy

To confirm the totalized flow accuracy of the SLA Series mass flow meters, Brooks Instrument used a Bell-Prover (traceable flow calibration standard) and a formal totalizer verification process. With this approach we were able to demonstrate totalized flow accuracies of better than 1.2%. The chart below summarizes the data for 12 devices each run at four (4) flow rates.

Brooks Mass Flow Meter Error Rate Date

 

 

 

 

 

 

Brooks Instrument SLA Series mass flow devices are available with a variety of digital communication protocols and a range of options to satisfy even the most difficult applications including hazardous area and outdoor installations.

To learn more about our proven mass flow devices for gas usage monitoring or any other application where totalized flow is required, please contact us.

Using LabVIEW™ Software to Interface with Brooks Instrument Thermal Mass Flow Controllers

September 15th, 2016 No comments
brooks-gf40-mfc-labview

Brooks Instrument Model GF40 MFCs (qty 4) with Multi-drop Cables

LabVIEW™, a National Instruments software development tool, is widely used to create software applications that monitor and control a variety of sensors and control devices. It is very common to find a laboratory, university, or a pilot manufacturing plant using one of these applications to interface with mass flow devices. LabVIEW™ software can interface with a Brooks Instrument mass flow device through different forms of data acquisition. The most popular forms of data acquisition used with Brooks Instrument mass flow devices are described below.

Analog Signal Interface

The chances are good that LabVIEW™ software users have analog to digital I/O cards, and can run their MFCs utilizing the 0-5 volt or 4-20 mA analog signaling via LabVIEW™. This is recommended for anyone who may not be ready to move to direct digital control.

national instruments power supply

Power Supply by National Instruments

RS485 Digital Signal Interface

Brooks Instrument mass flow devices configured with the ‘S’ communications option provide RS485 digital communications via the 15-pin D connector. The RS485 digital signal can be passed directly to the computer running LabVIEW™ through a serial RS485 converter. The GF40, GF80 and SLA Series MFCs from Brooks Instrument can be configured with the ‘S’ communications option.

    • Brooks Instrument provides a free set of VI files for use with LabVIEW™ software via our website which can be loaded directly into the LabVIEW™ application, and provide the building blocks for creating a LabVIEW™ software control interface utilizing the S-Protocol digital command structure. Additionally, a Brooks LabVIEW™ DLL file is included so these building blocks can be referenced and used within a LabVIEW™ application program interface (API).
    • Another possibility is to use the Brooks Instrument Smart DDE (Dynamic Data Exchange) software as an alternate tool to create links between the LabVIEW™ application and the GF40, GF80 or SLA Series flow, control, and configuration parameters. Additionally, the user can leverage Windows applications (Excel, Word, Access) and programming languages ( C++, C#, Visual Basic) and SCADA programs from suppliers such as Allesco and Millennium Systems International. No knowledge of the mass flow device S-Protocol command structure is required. With Smart DDE, the user gets direct access to the required data fields. This is not a 100% turnkey solution, but reduces the amount of coding required to communicate with and control the MFC.

DeviceNet Digital Signal Interface

GF40, GF80 and SLA devices configured for DeviceNet digital communications can also be controlled via the LabVIEW™ application. Note that this requires a National Instruments DeviceNet interface card and associated drivers and software, which provide support for developing application interfaces using LabVIEW™ software for Windows and LabVIEW™ Real-Time. The following is taken from the National Instruments website:

National Instruments DeviceNet for Control interfaces are for applications that manage and control other DeviceNet devices on the network. These interfaces, offered in one-port versions for PCI and PXI, provide full master (scanner) functionality to DeviceNet networks. All NI DeviceNet interfaces include the NI-Industrial Communications for DeviceNet driver software, which features easy access to device data and streamlined explicit messaging. Use a real-time controller such as PXI and NI industrial controllers to create deterministic control applications with the NI LabVIEW Real-Time Module.

So, don’t be afraid to go digital. The digital aspect of our mass flow devices include many on-board functions that work in the background and make the device superior even if the final flow signal is sent via analog signal (0-5 Vdc or 4-20 mA).

Successfully Managing Industrial Chlorinated Processes with Metal Sealed Mass Flow Controllers

August 9th, 2016 Comments off

Chlorine (CL2)Chlorine (CL2) is a member of the halogen elements group that is highly reactive and bonds easily with hydrogen to form HCL acid. HCL attacks stainless steel aggressively – literally passivating the surface of the stainless steel, and can render a thermal mass flow controller inoperative in a brief period of time. CL2 is used frequently in many applications from making PVC pipe and treating water to plasma etching a computer chip. CL2 is a critical process element in our world. CL2 mass flow controllers typically have a significant life span reduction which can be improved using tightly managed process controls. So what needs to be controlled in a CL2 process?

1) Leak test your system
The primary contaminant component for CL2 applications is air and its entrained moisture (water) content. To avoid this process “invasion” it is imperative that the entire system be leak tight at the onset of work. The best (and cheapest) way to do this is to pressurize the line with clean, dry nitrogen (N2) to 50 PSIG. Make sure the line is not blocked in any way with shut off valves, etc. Measure the line pressure as accurately as possible and allow the piping to stand in a static mode for a 24 hour period or longer if possible. Recheck the pressure reading to verify no decay has taken place. It is best to verify leak integrity in a temperature stable environment.

2) Pump purging before every start up and after every process run
Eliminating air content in the process line before CL2 is introduced is essential to a successful startup procedure. Purging the process path after a process run will further enhance the longevity of your CL2 mass flow controllers. Cycle-purging using dry N2 is the best method to accomplish the purging process. This is accomplished by raising the N2 purge gas line pressure to 30 PSIG and then exhaust to a small backpressure of 1-3 PSIG. This backpressure will protect the process line from back flow of air. This process should be repeated at least 15 times to evacuate as much air or other moisture bearing gas from even the smallest dead space in the line. Maintaining a high vacuum state in the process line after this this cycle- purging is completed will qualify a “clean” system for CL2 service.

3) Eliminate the possibility of contamination from the N2 purge source
The N2 purge source should be certified to have less than one part per million (1 PPM) of moisture/O2 in it. This should be verified periodically with in situ testing. It is best to use a dedicated N2 purge gas line for CL2 services. Ideally, specialized gas purifiers (as used in the semiconductor industry) should be used just prior to the point of process gas use as a primary precautionary method. These purifiers are a necessity to achieve better than 100 parts per billion moisture content which is the recommended “safe” level to minimize / eliminate the production of hydrochloric acid in the process stream.

4) Use the appropriate/best mass flow controllers for CL2 service
The ideal thermal mass flow controller for CL2 gas service is the Brooks Instrument metal sealed GF80 Series or GF100 Series. Metal seals eliminate the possibility of outgassing thru elastomeric o-rings, keeping air out of the flow stream. These products have essential functional components made of Hastelloy C-22 – flow sensor, valve seat, and valve orifice. Hastelloy C-22 is inherently corrosion resistant to CL2. Additionally the GF80 Series and GF100 Series products have a 10µ inch Ra surface finish or better for particle free function. The exceptional performance of the GF series is enhanced by our MultiFlo™ technology – gas and range programmability embedded in the electronics of each device. Actual CL2 gas was used to establish an empirical CL2 gas calibration table inherent in every GF Series product. The GF80 and GF100 Series will exceed your expectations for the best accuracy and performance in your CL2 application!

Are there direct replacements for Full-View® glass tube flow meters (models 1110, 1114, 1140, 1144)?

July 25th, 2016 Comments off
Full-View Glass Tube VA Flowmeter

Full-View® 1100 Series

With the obsolescence of Full-View® models 1110, 1114, 1140 and 1144, we are often asked for a direct dimensional flow meter replacement. The GT1306 (127,150mm) and GT1307(250mm) retro-fit meters will accommodate the same fit, form and function as the existing meters. Please note you will need the following information to complete a sizing and model configuration:

  • Original sizing and flow specs
  • Overall length and center to center dimensions
  • Connection type: either NPT or Flange and the orientation of the connections
  • Elastomer compatibility

You can access more details on replacement options here.

Three Brooks Instrument products recognized in 2016 Control Readers’ Choice Awards

July 8th, 2016 Comments off

Control readers have great taste: Once again, they recognized the performance, accuracy and reliability of several Brooks products by awarding us top rankings in two categories (and third-place ranking in another) in the 2016 Control Magazine Readers’ Choice Awards.

We were recognized in three categories: Top choice for variable area flow meters and positive displacement flow meters and third place for thermal mass flow meters. That makes NINETEEN years in a row that our VA flow meters have been named 1st choice by more than 1,000 automation professionals surveyed.

Winning this award has always meant something special to us here at Brooks. It’s chosen by the end-users of our instrumentation, and they are asked to compare our performance with our competition, so when they award us top ranking it validates our hard work and our constant focus on delivering the finest technology in the industry.

Thanks to Control and a special thanks to the readers of Control Magazine for your votes!

Download the complete 2016 Readers’ Choice Awards article.

Understanding Mass Flow Controller (MFC) Accuracy

June 14th, 2016 Comments off

Accuracy EquationOne of the key factors typically considered when selecting a measurement device, such as a mass flow controller (MFC), is accuracy. Anyone who has researched Mass Flow Controller accuracy likely knows that there is a wide variety – both in how accuracy is stated and the device performance.

So how does anyone make sense of this variety of accuracy statements? Let’s start by looking at the three basic building blocks of accuracy:

  1. Calibration and Measurement Capability (commonly referred to as CMC)
  2. Repeatability, and
  3. Linearity

The first element, CMC, relates to the equipment and process used to test devices, while repeatability and linearity are related to the device itself.

CMC
In short, CMC is a measure of how closely the calibration method represents “truth” or absolute accuracy. No calibration equipment or method can perfectly reflect “truth”; therefore, the uncertainty associated with CMC is always >0. CMC captures both the inaccuracy of the components of the calibration system and the statistical variation during its use.

For more information on CMC, visit: http://www.isobudgets.com/know-cmc-uncertainty/

Repeatability
This represents the device’s ability to repeat a flow measurement under the same conditions in a short period of time. If an MFC was used to create a specific flow rate over and over again in rapid succession without changing conditions, the distribution of the flow measurement data points (in excess of the variation in the CMC) would indicate the repeatability of the MFC.

Linearity
This element is needed because all Mass Flow Controllers are inherently nonlinear to some degree. To account for this, a curve-fit correction is applied to the devices. This is accomplished by collecting multiple data points during a calibration process and determining a curve fit equation. Linearity indicates how well the curve-fit correction worked.

Each of these building blocks contributes some amount of uncertainty to the accuracy of an MFC. The sum of those uncertainties equate to the device accuracy.

Accuracy = CMC + Linearity + Repeatability

All of these factors impact the accuracy that you see on the spec sheet for an MFC or other measurement device. Other factors, such as long-term stability, conversion factors, temperature/pressure coefficients and process conditions vs. calibration conditions impact the actual process accuracy.

To get an apples-to-apples comparison of MFC accuracy, it is important to understand the above elements of accuracy and how they relate to the device specifications. Some MFC manufacturers include all three elements in their accuracy statement, some do not. For assistance selecting the most accurate MFC for your application, please contact our Applications Engineering team or your local Brooks Instrument representative.

Sparging with Mass Flow Controllers Makes Wine Taste Better

May 23rd, 2016 Comments off

Sparging is injection of a gas into a liquidMerriam Webster defines sparging as: to agitate (a liquid) by means of compressed air or gas entering through a pipe. A simpler explanation is: sparging is the injection of a gas into a liquid. The method used to expose the gas to the liquid varies and these systems are called aerators, bubblers, carbonators, diffusors or injectors. The most recognizable example is the bubbler in a fish tank.

Where Sparging is Used
The sparging of CO2 and O2 in bioprocessing controls the pH and dissolved O2 levels required to maintain the ideal fermentation environment in bioprocessing. The control of the pH by sparging is also utilized in water treatment and many refining processes. Removal of contaminants that are absorbed by a sparged gas (stripping) is critical in many medical and purification applications.

Sparging in the Food & Beverage Industry
Though sparging applications are plentiful in many industries, the applications in the food and beverage industry impact our daily lives. Carbonating sodas and beer is an obvious application. Spargers are used extensively to lower the O2 content in order to increase the shelf life of juices, oils and processed foods. The injection of gases for foaming or increasing bulk volume is common in dairy processing and can be seen on the store shelves as whipped or light. Here in California wine country, sparging is critical to controlling the oxidation processes that determine the subtle variations in wine taste and aroma.

The Need for Precision Flow Control When Sparging
The benefits of controlling critical process variables to tighter ranges are driving the need for precision flow control in sparging applications. Brooks Instrument supplies products that measure the sparged gases and controls the rate that the gases are exposed to the liquid. Our SLA5800 Series Mass Flow Controllers & Meters (MFCs) offer high accuracy over a wide range of flows and pressures, while the SLAMf Series Mass Flow Controllers & Meters are engineered with a NEMA4X/IP66 enclosure for installation in environments where dust, moisture, temperature extremes or wash-down requirements are an issue.

Is your MFC displaying/outputting a flow signal (or negative flow) with no gas going through the device?

April 19th, 2016 Comments off

There are many reasons why this can occur, such as a change in mounting orientation, ambient temperature, or process pressure. While mass flow controllers (MFCs) from Brooks Instrument are known for stability and minimal long-term drift, the flow signal or process variable (PV) from an MFC may drift over time.

To ensure the best possible accuracy, it is recommended to zero the MFC at initial installation and periodically thereafter. The best way to know when your MFC needs to be re-zeroed is to see if there is flow signal (positive or negative) at a zero flow condition. Keep in mind, MFC valves are precision control valves, not positive shut off valves, so a small amount of valve leak-by may exist.

To zero your device, it is recommended that you follow these steps:

  • Allow for a warm-up time of at least 45 minutes to get to normal operating temperatures
  • It is preferable to zero at process conditions (meaning inlet pressure should be the same as the normal device operation)
  • Close a downstream shutoff valve and open the MFC valve using a setpoint or valve override (VOR) open command. This will fill the lines up to the shutoff valve and pressure will equalize across the MFC.
  • Allow 30 seconds minimum for stabilization
  • Monitor the output (PV) signal
  • For digital devices, press the zero button until the LEDs indicate the device is re-zeroing. The LED indicator turns green when the zero process is complete. PV signal should be at zero. Repeat if necessary.
    • Alternatively, digital devices can be re-zeroed using service tools (BSS or BEST) from Brooks Instrument.

Zero Button on MFC

  • For analog devices, monitor the output signal and adjust the zero potentiometer until zero is achieved.
  • Remove VOR open command and/or set point
  • Open the downstream shutoff. Monitor the PV for any flow indication. If you are seeing flow, this could be the valve leak-by as described above.

Brooks Instrument MFCs are zeroed at the factory. An initial zeroing may be necessary upon installation. By setting up the device, as outlined in the first five steps above, you can determine whether an initial zeroing is needed, or if it is good to go.

If you need assistance please contact our Technical Services team or your local Brooks Instrument sales representative for assistance.

How to Set-up Multiple MFCs in an RS485, Multi-drop Network

March 2nd, 2016 Comments off

Many options are available when setting up an RS485 network. The goal, of course is to get better control of your system. There are some solutions that make setting up both small and large RS485 networks easy. Digital MFC’s and electronic pressure controllers from Brooks Instrument include an RS485 communications option, typically utilizing the Smart protocol.

Small Networks – Less Than 10 Devices For a smaller network of less than 10 devices, a simple non-powered, USB-to-RS485 converter can be utilized. However, here, we will show an off-the-shelf turnkey solution that uses a powered converter. An example of a turnkey solution is:

•Brooks Smart Interface software, and
•0260 power supply/converter

RS485 Network Set-up for Less Than 10 MFCs

Large Networks -10 or More Devices For a larger network of 10 devices or greater, a powered converter should also be selected for best performance results. The 0260 power supply/converter from Brooks Instrument along with the Smart interface software can control up to 30 devices. Both of these products will communicate with any Brooks Instrument MFC or electronic pressure controller with the RS485 Smart Protocol, such as the GF40, GF80 and SLA5800 Series. Other than the 0260 power supply, the only piece of hardware required to set up the network is a multi-drop cable. The images below show different ways to set-up a network with more than 10 devices. RS485 Network Set-up for 10 or More MFCs The Brooks Smart Interface software and hardware will work independently. For users that have their own software tools, the 0260 hardware can be used as a power source and signal converter. Additionally, the Brooks Smart Interface software can be used in conjunction with hardware already in place. RS485 Network Optional Set-up for 10 or More MFCs If you need assistance setting up devices in an RS485 network, please contact our Technical Services team or your local Brooks Instrument representative for assistance.

Liquid Level Measurement Using the “Bubbler Method”

January 29th, 2016 Comments off

Liquid Level Measurement Using the Bubbler Method
Industry
General chemical industry applications where liquids are stored in tanks.

Application
Measurement of the level of a liquid in a tank using a pressure transmitter to measure the pressure created by the weight of the liquid. The key feature of this method is the use of a small diameter (typically ¼”) tube installed in the tank to allow the pressure measurement to be taken at the top of the tank, eliminating potential leak points at the bottom of the tank.

Process Details
The pressure measured at the bottom of a tank of liquid will be proportional to the level of the liquid in the tank according to the relationship:
Height of liquid = Pressure at bottom of tank / density of liquid.
To avoid possible leak points, the pressure measurement can be taken at the top of a “dip tube” installed in the tank as shown in the diagram above. The key to this method is the introduction of a low rate of gas flow in the tube, effectively transferring the pressure at the bottom of the tank to the inlet of the tube (plus the small pressure drop created by the flow rate in the tube).
To keep the pressure drop low in the tube, a flow rate of 1.0 SCFH is typical for a ¼” diameter dip tube. This minimizes the offset in the level measurement created by this pressure drop.

Instrumentation
Using a Brooks Instrument Model 1350G purgemeter with a Model FCA8900 integral downstream flow controller will keep the flow rate constant in the dip tube with the varying downstream pressure caused by the varying liquid level. This further improves the accuracy of the measurement by keeping the offset constant.
The supply pressure to the flowmeter should be set to a value high enough to overcome the back pressure of the liquid level and the minimum pressure drop needed across the flow controller. A supply pressure of 25 psig would be adequate for tank levels up to 30 feet. The flowmeter scale should be sized (i.e. compensated) for this supply pressure.

Also available from Brooks is the SolidSense II® pressure transducer for the primary electrical output.
Brooks Instrument has been a supplier of choice for this application for many years, and to several industries, including petroleum refining, electrical power and semiconductor.