Scale-Tron, automation, sensors and weighing systems

AQUASENSE FAQs - frequently asked questions re: moisture

Can I take a sensor calibrated for sand and use it on other materials?  Can I use AquaSense's sampling feature for on-the-fly batch correction?  Which is the best output choice, 0-10 volts or 4-20 mA?  My material is hot.  Can I use AquaSense in this case?  This page answers these questions and others.

Is the AquaSense sensor ready to use when I get it?  It depends on your application and the material.  Unless we are told differently, we pre-calibrate AquaSenses for use in bins of sand, as used in concrete production.  This sand is never exactly the same as the sand we use in our calibration lab.  Its density and grain size can vary widely, giving an error on any type of moisture sensor when used out of the box.  We have seen differences as much as 4% in different samples of building sand.  You should always check the accuracy of any moisture sensor against an oven-dry test as soon as possible after installation;  if time is short, a single test and a quick trim of the span control will correct most of the error.  Further oven dry tests at your minimum and maximum moisture levels will confirm accuracy across the whole working range.

No moisture sensor is accurate in all materials.  They must all be checked after installation.

I hear that your sensor is harder to calibrate than other.  Is this true?  It depends on what accuracy you want to get.  Others claim that you can merely use a bucket of water for calibration.  This is inaccurate because the measurement must be made on a combination of water, sand and air to produce the exact dielectric constant that the sensor measures.  There is no shortcut - use at least two samples and preferably more, with both dryer and  wetter materials.

We always recommend the most accurate method, to ensure your satisfaction with the results.

Can I take a sensor calibrated for sand and use it on other materials? Sometimes yes, sometimes no.  If the material is similar to sand (density of 80 to 150 lb per cu. ft.) and moisture range is 1 to 20% full scale, there should be no problem, AS LONG AS YOU RECALIBRATE IT!  If its density or moisture range is widely different, however, you may not have enough adjustment range.  Ideally, you should contact our plant for advice.  If the sensor has not been shipped, we can set it up for the material;  we have many samples already and we test new materials every week.  If we have no experience with your material, we will ask for a sample.  This ensures that your sensor will not only work but will be approximately precalibrated when you receive it.

If you have a range of materials, each with its own sensor, they should all be set up in this way.  If you need to keep a spare sensor for replacement, it may be suitable for some but not all of the materials.  Again, call us for advice.

Our advice is free - take advantage of it before you take delivery.

Can I use AquaSense's sampling feature for on-the-fly batch correction? Some batch controllers correct the aggregate target weights on the subsequent batch, based on the moisture value measured on the previous batch, while others recalculate the target during the weighing period, based on the current moisture value.  Both systems have their merits and both can use the "sampling" mode of operation.  The moisture average is started when the feed gate opens and continues during the fast and slow or jogged feed.  The analog output is updated continuously and a reading can be taken at any time.  This is much better than using the "continuous" mode, which has a built-in response time of several seconds that limits the accuracy when immediate results are required.

The SAMPLING mode is the best for both on-the-fly and next batch measurement.

Which is the best analog output choice, 0-10 volts or 4-20 mA? Both have their place and many times you don't have a choice.  Most of the North American batching computers use the 0-10V standard while most PLC based systems (like our BatchTron) use 4-20mA.  Unless you must choose the 0-10V standard, always use 4-20mA;  it is slightly more accurate, especially over long cable runs, and allows connection of both the batch controller and the digital display if needed (in series).  The digital display requires 4-20mA as its power source and will not operate on 0-10V.

Always use 4-20mA when you can.

Is AquaSense's digital connection compatible with my batching controller?  Both the RS232 (one sensor only) and the RS485 (multiple sensors on one line) use the same protocol, which is "industry standard".  If your control system is already compatible with others using digital connection, it will connect to AquaSense  and operate in the same way as with other sensors.  The setup and calibration software uses a different protocol however, and you need to install the Scale-Tron GUI software in order to change adjustments.

AquaSense  uses 'Industry Standard' protocol and is compatible with most controllers.

My material is hot.  Can I use AquaSense in this case? AquaSense is rated for temperatures up to 120 degrees F (50 degrees Celsius).  Above this temperature, accuracy will be impaired and above 200 deg. F ( 93 deg. C), the electronics will cease to function.  You can protect the sensor by installing it in a tube, mounted within the bin, at our recommended angle and insertion depth.  The tube must be sealed to the outer rim of the sensor at its far end and be wide enough to allow free circulation of air. A free circulating or forced air supply should be provided to keep the AquaSense body temperature as low as possible.  In extreme cases, replace the air tube with a 1/4" to 3/8" copper water pipe coiled around the portion of the sensor inside the bin.  The ceramic faceplate can be allowed to reach 100 deg. C. continuously but above this temperature the silicone sealant will deteriorate.

These techniques will allow operation in steam heated aggregate bins and in hot foundry sand, plus many other applications.  Call for more details or download application note.

Hot materials require special installation precautions.  Call us.

Can I install AquaSense on a conveyor?  It's possible, by using our "Glider" sensor mount, but you won't get the accuracy that you can get when it is installed in a bin.  For this reason, we suggest that you try to locate it in the bin that feeds the conveyor if possible.  A second alternative exists if the conveyor feeds a second belt, when you can install a chute between the two.  Make the opening of the chute onto the lower belt too small to accommodate the flow and allow it to purposely overflow at its upper end, directing the overflow again onto the lower belt.  The chute will pack the material, making accurate measurements easy.  Call us for full details.

How can I view the moisture in several bins simultaneously? The simplest way is to use a separate digital display for each sensor.  The panel-mount sensor is suitable for installation in a small cabinet or large control panel.  Alternatively, a single display can be used for many sensors with a rotary  switch which selects one bin at a time.  If a computer display is desired, the RS485 conection can easily connect all the sensors together, into a single serial port on the computer or PLC, but you need to develop some simple software to use it.  Alternatively the calibration and monitoring software can read all the sensors continuously.  Call us for advice if you need something a little different.

Whichever way you want to do it, it is simple.  Call us for details.

How can I monitor moisture in a single bin that holds several different materials from time to time?  The AquaSense can be calibrated for many different materials.  These calibrations are stored in the sensor's memory and can be retrieved through the digital RS232/RS485 connection.

AquaSense solves problems that could not be solved before.

Why do my sensors burn out for no apparent reason?  Several customers have had premature failures of their AquaSense sensors;  typically the circuit board shows burn marks under one or more chips, plus the microwave sensor is damaged.  This is most likely due to a poor ground connection between the control cabinet and the plant frame.  Voltage surges (usually due to nearby lightning) entering the cabinet through the power or phone lines find the shortest path to ground, which is through the AquaSense or load cells.  The solution is to install a short, thick ground conductor between plant frame and control cabinet to hold both at the same electrical potential.  No sensor is immune to this type of damage, but it can be minimized.

See our Tech tips page for more details.