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The Load Cell Source |
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1-800-899-9988 |
690 Discovery Dr. N.W., Huntsville, AL 35806 |
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What is the Scale Sentry®? Scale Sentry® gives your existing scales the ability to constantly
monitor themselves for scale accuracy. It monitors both the overall scale (load cells and
digital indicator / signal conditioner) as well as each load cell individually. Errors in
excess of 5% are immediately detected and alarmed for. How does the Scale Sentry® work? It is like having many digital volt meters constantly monitoring the
ratio of mV signals from each load cell, and the excitation voltage. When a problem occurs
greater than 5%, an alarm is activated. On tank scales the monitoring is constant. On
Truck - rail and platform scales, the mV signals are monitored when the scale is at dead
load zero (jumper selectable). Does the Scale Sentry® need calibrating? Yes, after installation, the scale is checked using the normal
calibration technique, (dead weights, transfer standards, etc.) At that time, reference
potentiometers are adjusted which define the tolerance band aperture of the load cells -
mid point of span and the excitation voltage window. How long does adjusting the pots take? Typically about 15 minutes. What does the Scale Sentry® look like? An IP67 / NEMA 4X box 5x8x3 inches tall with three external cable
glands. The optional switch selectable summing junction box is the same size. Can I keep my existing junction box? Yes, your existing junction box can be used, however an additional
cable glad must be installed. The optional switch selectable summing junction box provides
the ability to quickly and easily diagnose the cause of a problem, and on non legal for
trade symmetrically loaded scales, the ability to turn off a defective load cell which
removes it from both the excitation and averaging circuits, thereby keeping the scale on
line while a replacement load cell is located and/or installed. Why would I need the Scale Sentry®? Because we live in an imperfect world - load cells are finite
devices with limited life cycles. When load cells fail, they cause major errors (which
cost the user lost production and degrade the quality of your product) Scale
Sentry® notifies you immediately when serious problems occur, and helps the
technician to quickly locate the problem. Will Scale Sentry® enhance the quality of my product? Absolutely! Undetected scale error downgrades the uniformity of
quality in products. ISO 9000 and other quality systems strive for uniformity. Scale
Sentry® is ideal for any weighing system which is part of an ISO 9000 system. How can Scale Sentry® improve ISO 9000 quality performance? Most ISO 9000 scales are checked yearly, semi annually, quarterly
ore even monthly. However, load cells can fail at any moment and cause error. Scales are
used daily to produce product, therefore to meet the true meaning of ISO 9000, the user
needs to know that the scales are accurate every time they are used. Scale
Sentry® provides this assurance! How can Scale Sentry® help pay for itself? Lost production from scale downtime can cost hundreds or thousands
of dollars per hour. In that it notifies you the instant a scale has a problem and guides
the technician to quickly repair the problem, down time is greatly reduced. This reduced
down time increases productivity and profitability. Scale Sentry® also
eliminates product giveaway caused by scale errors. Lastly, don't forget the all important
built in spare load cell feature for non legal for trade symmetrical scales. Can Scale Sentry® be added to any multi load cell scale? Yes, Scale Sentry® can be added to any make of
scale using mV output load cells. Do I have to replace my existing load cells or digital indicator? No - only the summing junction box needs to be modified or replaced. What type of problems will be detected? Shorts, opens, grounds, intermittent problems, non linearity of load
cells, power supply instability, mechanical binding and even logical errors. What do you mean by logical errors? Errors which would be overlooked if only the summed signal was
analyzed. For example, an accurate scale might output 25, 25, 30 and 35 for a total of 115
pounds of summed weight. If the load cells were to drift to 20, 20, 40 and 35, the
summed signal would be the same, however the change causing error would be detected. How small an error can be detected? The normal tolerance window is set at 5%. The window can be adjusted
up or down. Note: Total failure of one out of four load cells typically causes a
25% error. One out of eight causes a 12.5% error. What will happen when an error is detected? The Scale Sentry® will activate a LED alarm light
on the outside of the box. It also provides a contact for an external alarm. How will I know what causes the problem? An LED on the outside of the Scale Sentry® will
identify the cause of the erro4r as either load cells or power supply. With the optional
patented switch selectable junction box, test points allow switch selection and reading of
the millivolt output of each load cell individually. Will I know the magnitude of the error? The Scale Sentry® will not trip if the error is
below the set 5% window. Can I disable the alarm condition? Yes. The Scale Sentry® only notifies you that an
error causing the problem has occurred. An external switch disables the alarm. Can the Scale Sentry® automatically fix the problem? No. Only a qualified scale technician can repair a scale. Will the Scale Sentry® allow for temporary repair by disconnecting a bad load cell? The optional patented switching junction box can remove a defective
load cell from both the excitation and averaging circuitry, thereby returning the scale to
an acceptably accurate status. This may not be done on legal for trade scales. This works
like having a built in spare load cell. The more symmetrical the scale, the better the
accuracy. Can the Scale Sentry® be used on non symmetrical scales? Yes - it will "learn" the scale's non symmetrical ratios,
within the 5% tolerance window. Can the Scale Sentry® be used on Truck - Rail and platform scales? Yes. A thorough scale analysis will be conducted whenever the scale
is empty. Note: Many scale errors are positive which cause the digital indicator
to show weight when the scale should be at zero. It is a common practice for the
weighmaster to merely rezero the scale. This makes the display show zero, however merely
masks the scale error. Scale Sentry® would detect this error and alarm. Can the Scale Sentry® be used in a hazardous environment? Yes. There are two options. Option #1: The Scale
Sentry® can be located in a safe area and connected through current limiting
barriers. Option #2: The Scale Sentry® can be placed in an
appropriate NEMA 7 or 9 enclosure. Is the Scale Sentry® FM Approved? Yes, with the appropriate class group and division enclosures or
safe area installation. Can the Scale Sentry® cause error in my scale? No. The Scale Sentry® is a passive device. Can a problem with the Scale Sentry® cause my scale not to work? No. Should a problem occur, a failure LED will light, indicating a
problem in the Scale Sentry®. This will have no effect on the scale. Are there other products like the Scale Sentry®? No. The Scale Sentry® is both patented and patent
pending technology. There are so called "digital' systems which necessitate the
replacement of the load cells and all of the instrumentation. These type systems are not
only much more expensive to buy and necessitate costly installation, they are less capable
in that they cannot detect logical errors.
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