Emerson Exchange 365

8732 FF Flowmeter show 3.5 m3/h while pipe is empty

Hi Guys

I'm working comissioning a new copper concentrator and we have an issue with a 8732 fieldbus magnetic flowmeter (size 1/2"), the device is new and has never been used before. When I powered up the device  the local display shows a reading of 3.5 m3/h (URV is 5 m3/h) but the pipe is empty (process fluid is fresh water). I've read about performing the AUTO ZERO function but  I'm not sure about it. My question is if  performing the AUTO ZERO method is going to solve the problem or what else should I do?

NOTE: I'm not going to be able to test the device with water running trough the pipe until next month because there is no water upstream

Thanks in advance for your help

Regards

Diego 

• flow transmitter
• flow meters
• Flow
• mag meter
• electromagnetic flow transmitter error
• calibration

dbarrigac

• 6 Sep 2015 5:06 PM
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5 Replies

• leirbag

  

  • 7 Sep 2015 6:50 AM

  Hi dbarrigac,
  All the magnetic flowmeters will show different flow values on empty pipes, without "Empty Pipe Detection" activated and this function configured to show 0 and and warning message (or a discrete outout activated to changhe its state). Therefore look and activate this function in your transmitter. Something's wrong if your pipe is full of water and you're sure that the liquid does not have the circulation, with no zero flow indication. If the pipe cannot be filled with water, please remove the flowmeter, submerge the sensor (and only the sensor) in a container with water and power up the transmiter. Look at the display indication must be zero.

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• Mike Schaefer

  

  • 8 Sep 2015 3:49 PM

  In reply to leirbag:

  Submerging the sensor in a container of water is not a good practice. Sensors aren't rated for submergence in that manner. It is possible to have the water leak behind the liner and cause a sensor failure. Sensors are rated for submergence based on both process connections being fully connected and tightened to specified torque values. The proper method for filling a uninstalled sensor is to cap one end with a blind flange. Also keep in mind that the uninstalled meter will need a process reference ground connection (ground strap, ground ring, or ground electrode) for obtaining a good zero flow measurement.
  
  In regards to the AUTO ZERO function, that is only required when the coil drive frequency is changed from 5 Hz (default) to 37 Hz. The AUTO ZERO function will not run if the coil drive frequency is set to 5 Hz. The first thing to try for solving your issue is to activate "Empty Pipe Detection". The next thing to verify is that there is a proper process reference ground connection. You can refer to the installation section of the manual for process reference connection techniques - http://www2.emersonprocess.com/siteadmincenter/pm%20rosemount%20documents/00809-0100-4444.pdf

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• leirbag

  

  • 9 Sep 2015 6:46 AM

  In reply to Mike Schaefer:

  Hi Mike,
  I want to know were is indicated in Emerson documentation to not submerge the sensor. First of all, a 8705 sensor (I'm using frequently this type) is rated IP68. How is damaged the sensor with few drops of water (if the event occurs)? I confess that, over 20 years, I submerged many flowmeters ( I had no blind flange available), for a short time, it's true, and for testing purpose . I have "dissected" once a Fisher Porter sensor. The only way to penetrate for the water drops through liner and the tube wall, inside the sensor is  the mounting hole for electrodes. Due to the conical shape of the electrode and the fact that the hole in the liner is less than that of the tube plus special sealing elements, this possibility is excluded. I happened once that process fluid to penetrate the sensor and destroy it. That happened because a man confused in assembling the material from which the sensors must be installed. The fluid was sodium hydroxide solution. Emerson changed the flowmeter.

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• Mike Schaefer

  

  • 9 Sep 2015 2:37 PM

  In reply to leirbag:

  I don't think it is stated anywhere in the product documentation not to submerge the sensor in a container of water. That said, the IP68 rating is based on the sensor being fully installed, including proper conduit entry seals. That is how the meter was tested to obtain the IP68 rating. In addition to that, some designs of the 8711 sensor are not IP68 rated.
  
  You correctly identified the main concern (and potential failure point) of submerging a meter without end caps. While a failure is highly unlikely, it is still possible. Most liner materials will serve as a sufficient enough seal to keep water from leaking behind the liner in a low pressure submergence situation, but PTFE liners don't seal to the tube wall at all so they would be the most susceptible. I can't comment on the electrode design of the Fisher Porter sensor, but once fluid is behind a liner, there is a possibility for it leak into the electrode hole opening in the tube wall. Again, the failure is highly unlikely, but possible.
  
  In my previous response I was trying to promote BEST practices which would not lead to the potential (be it ever so small) failure of the sensor.

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• leirbag

  

  • 10 Sep 2015 6:48 AM

  In reply to Mike Schaefer:

  I agree with you it's the best practice, the risk is zero. On the other hand, if it is possible that a few drops of water to penetrate into the mounting hole, through the metal wall and liner, at this low pressure, I'm 100% sure as well will penetrate the product drops between the electrode and liner at much higher pressure. The sealing is like this: metal wall - liner - electrode material - liner - metal wall. Space between metal wall and liner means space between liner and electrode. I'm using 90% of magnetic flowmeter with PTFE liner. The real danger of water penetration between the tube and the liner is not water itself, but it's  possible contamination with traces of corrosive substances from the flanges (if we are talking about long used and dismantled flowmeter). The best way to prevent accidents  It is to warn customers about such a situation (to complete documentation with informations about dismantled flowmeters).There is not only one suggestion that I can make, I like Emerson flowmeters, but there are some design mistakes. I recently saw the "3 buttons " procedure to lock software the 8732 display, it's an improvement, not the best way. The safe way is to eliminate the front hardware lock switch (it's complicated and It  can go wrong to remount the display) , and to put another one into the rear compartment, near the power supply and signal connections, with another hardware function : to deactivate optical buttons.

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