Tuesday, September 4, 2012

Process Automation System Problem Solving

Application Note on Read First Worry later, or Struggle first and then read the manual later, Radar Level Measurement with FMP40’s – solving the unseen problem

Have you ever rushed to apply an instrument and failed to read the manual. If you are like most people you will follow the pictures in the manual before you read the details. It is also been said, “the Devil is in the Details.” If you ever built models as a child, you will know only to well how easy it is to put the pieces together and forget that one. Like the pilot in the cockpit for the model airplane, after you have glued the canopy in place. Recently on a service call for a manufacturer in the Michigan market an otherwise apparently simple installation became much more of an effort. The effort could have been avoided if only some specific details in the installation manuals were read / reviewed prior to the installation.
The level transmitter was installed in a wet well that collects rain water and is pumped to a local facility for treatment and eventual discharge. The installation was completed in the winter and all devices were working acceptably. It was not until the spring when the weather broke, the warmth of spring melted the ice, and the concrete structure went from dry to wet. As the concrete absorbed the moisture it also absorbed the sensor’s signal, and where it worked in January through March it no longer worked reliably in April.
Endress+Hauser offer’s the FMP40 Level transmitter for several applications, from metal tanks to concrete silo’s. In this case the sensor was installed in a concrete pit, with a 14” thick poured floor, the concrete was sleeved with a 4”PVC pipe that was 12” long, creating an issue with the bottom of the opening to the tank. This was necked down to a 2”diameter hole or so, and the cable went through the hole just fine. When the concrete was dry the sensor’s signal went through this short section with little noticeable reduction in operation. It was not until April and the wet cement, that the signal was knocked down to a level to low to return a good measurement.
In April the installing contractor contacted the system integrator about the sensor not working, and after a solid day or 2 of effort the contractor called in the manufacturer for assistance. Initially, from phone support the issue was not detected. After several field efforts to improve signal strength with the assumption of a good installation, the installation was again reviewed. It was then learned that the nozzle opening was not 3.5” all the way down as expected, and that the sensor cable was mounted 2” from a concrete wall.
Reading in the manual, the installation notes talk first about metal tanks, 4” minimum distance from a wall, then other applications, and finally liquid applications and concrete walls where recommended distances of 18” from the wall are preferred. The sensor was temporarily installed in a location in the middle of the wet well to verify the installation location was bad, and the signal increased 10 fold. Now the sensor was acting as expected. After this a new hole was cored in the concrete floor away from the all the walls and the sensor signal was 8-9 times stronger than originally seen in April.
Reading the manual although time consuming on this particular item could have saved the customer easily over 40 man hours of combined labor when travel time of all parties is reviewed (the General Contractor, the System Integrator, and the Company Representative.) For this application, the cost were not avoided, and they are unfortunately more significant than the 10 minutes of reading in the manual or review of the installation position prior to final concrete pour.
If you have an application question about an instrument installation, please contact Forberg Scientific’s Service Group and our staff will help you to resolve your issue, or connect you with someone who visit your facility and assist you.
If you have any questions our Services or Pricing please call Forberg Scientific Service Group at 248-288-5990. You can also contact Endress+Hauser at 800-642-8737.