temperature and velocity control of sandy air in duct

K

Thread Starter

khan

Hi,

actually i'm not a control engineer however my boss gave me a job to design the control system of a machine. In this machine there will be an air duct with 1 square-meter cross-section area and air will flow inside the duct with 29 m/s velocity at 70 celcius degree. Those are the upper limits, so velocity and temperature should be adjustable by a panel outside. One more thing, while air moves through the duct, sand will be mixed to the air at some point. I need to control the temperature and velocity of the sandy air at some point.

I am asking your suggestions that sensor types and models that can handle with those environmental conditions? I did my homework and found something on internet but it's always better to take idea of an expert if you don't know the job.

I know some about the control theory and programming PLCs. My controller will be Siemens S7 PLC. However, I really need some help at this point of selection sensors & actuators.

Any reply will be very appreciated. Thanks a lot.
 
Hi,

For temperature sensor, it should be kept in mind that high air speed and that too with sand mixed, causes erosion on outer sheath of thermowell.

For 70 Deg C, you can use RTD as temperature sensor with outer diameter of around 20 to 25 mm, with tungsten carbide coating to prevent erosion.
 
B

Bob Peterson

i would try to avoid doing any measurement after the sand gets mixed in, but I suspect this may well have a significant impact on air temperature as the thermal mass of sand is pretty high compared to that of air.

A lot depends on how you plan to control the velocity and temperature. If you are planning to use a blower with a VFD on it, it is pretty straightforward. Just adjust the fan speed as necessary. the air velocity can be measured where it is convenient.

The temperature control will be similar in nature, just that you will need a more robust sensor to deal with the sand in the air. A lot depends on how quickly it needs to deal with temperature and how tight the control needs to be. If you are firing up a burner as your heat source the burner control will be very typical of such burners. Only the sensor will be a little unusual because of the abrasive nature of the air stream.

--
Bob
http://ilbob.blogspot.com/
 
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