How do Digital Scales work, anyway?
All About Load
Cells?
Wiring your Junction Box?
Calibrating your
Scale?
Troubleshooting a Problem?
1. How do Digital Scales Work, Anyway?
Sophisticated digital weighing indicators, such as our animal weighing indicators, have additional filters that are capable of conditioning or stabilizing the electrical signal to account for animal movement, vibrations, etc.
Digital scales use a device called a load cell, which generates an analog electrical current when force is applied to it.
A digital scale is a remarkably simple invention. The more force, the more current. This current is transmitted to a digital weighing indicator, which converts the analog current into digital “counts” These counts can then be converted into grams, pounds, kilograms, etc., to represent the amount of force.
All About Load Cells
Their capacity can go well in to the hundreds of thousands of pounds.
- Single-point load cells: These are used for fine and very fine weighing applications such as lab scales. They are typically available in capacities ranging from 500lbs to 20,000lbs.
- Double-ended shear beams: These are most commonly used in larger platform scales, such as truck scales, group animal scales, etc. This current is then transmitted through the junction box and on to the indicator. There are numerous types and sizes of digital load cells, each one designed for a specific application. Once this analog signal reaches the indicator, an internal Analog/Digital conversion board converts the analog electrical signal to digital “counts.” These “counts” can then be converted to pounds, kilograms, etc. What is a load cell and how does it work? For most of our applications, we use what is called a single‐ended shear beam load cell. This type of load cell measures the downward force directly above the load cell foot. When force is applied to a load cell, it deflects (bends), which causes it to generate an analog electrical current. (see calibrating the indicator for more about digital counts). Some of the most common types include.
- Single-ended shear beams: These are most commonly used in platform scales, such as floor scales, small cattle scales, vet scales, etc. a. They range in capacity from 100lbs to several tons.
- Compression Load Cells (not shown in image): These are typically used for very large scales such as truck scales, rail scales, etc. They range in capacity up to about 75,000lbs each.
- S-Type or S-Beam Compression/Tension Load Cells: These are used in numerous applications, from hanging scales, to in-line tension/compression applications.
How do I mount the load cells?
No two platforms are the same, but as a general rule, you want the FOOT of the load cell as close to each corner as possible. Try to mount the load cells as far apart from each other as possible.
The load cells have a lot of extra cable. Can I cut it to make it easier to manage?
When load cells are manufactured, the electrical resistance along the length of the cable is factored into the overall signal strength. Never cut the load cell cables. If you cut the cable, you will have too little resistance and, therefore, too much signal. NO. Two words: ZIP TIES.
What if I cut the cables all the same length?
In theory, it will work. However, we do not recommend doing this, and cutting the cables will void your warranty.
Our standard load cells are made of hardened tool steel (we also have stainless steel load cells, but they’re very expensive and most people do not need them. However, we do not want the load cells to sit, submerged in standing water. If you’re in a Caribbean climate, you may want to consider them). Washing them down when you’re done weighing won’t hurt them but leaving them submerged will corrode the seals and they’ll start to pit. Generally, yes.
a. What is the junction box and why do I need one?
This is normally not necessary, but as your scale ages and the load cells begin to wear down, the j‐box will extend the life of your scale considerably. However, the advantage to using a j‐box is that they contain a tuning port that allows you to amplify or de‐amplify the signal from each load cell. In theory, you could also just twist all of the load cell cables together and wire them directly to your indicator, and the scale would work just fine. The junction box contains a simple summing card that aggregates the analog signal from each of the four load cells and passes it along to the indicator.
b. How do I wire the j‐box?
requently, the signal wires (Green and White) need to be reversed. See Troubleshooting for more about this. All j‐boxes are wired the same: EXC+ or E+ is RED EXC‐or E‐is BLACK SIG+ or S+ is Green SIG‐or S‐is White GND or SHLD is Yellow. We source our j‐boxes from several different suppliers so you may find that the wiring diagrams on our website do not match the j‐box that came with your scale or kit. Not to worry. These are used to control more advanced scale indicators. For example, if you installed your load cells with the arrow sticker pointing DOWN, you’ll need to flip the Green and White wires to reverse the signal. If your J‐Box has SEN+ and SEN‐, you can ignore them.
The Indicator
However, there are some basic commonalities between ALL digital indicators that are worth discussing in this document.. Each indicator should have its own user’s guide. The Indicator We sell a variety of different scale indicators that have specific features depending on your application.
a. How do digital scale indicators work?
A digital scale indicator converts that analog signal into digital counts. And, the amount of counts that are generated when there is, say, 200lbs on the scale, is 200lbs. As we said at the very beginning of this document, in question I‐a, a load cell measures force and sends an analog current to the indicator; the stronger the force, the stronger the current. When you calibrate a digital indicator, you are essentially telling the indicator that the amount of counts that are generated with NOTHING on the scale is ZERO pounds. Once you define these two values for the indicator, the internal logic board is able to do the math and figure out that the calf that is standing on the scale is causing the scale to generate a whole bunch of digital counts that equal 74lbs, for example.
- Zero Cal and Span Cal. The actual menu depends on your indicator (consult your manual) but the principle is exactly the same. i'e The indicator menu has two values that must be calibrated: Zero and Span. In the TR1NK indicator, it’s P5 and P6. In the BB8100SS Indicator and the TI‐500E Floor Scale Indicator, F16 is your Zero Cal and F17 is your Span Cal. In the BB7510 Indicator, C5 is your Zero Cal and C6 is your Span Cal. (Span means there is weight on the scale.) This is true for all digital indicators (some indicators have more than one Span Calibration, but it is generally not necessary to calibrate all of the Span points).
- You should try to use a Span Weight that is close to what you’ll actually be weighing. For example, if you’re weighing calves, try to calibrate your scale with about 150lbs. If you’re weighing bulls, try to use at least 1000lbs. This is not always feasible, but you’ll get more accurate weights if you use the appropriate amount of test weights. The State of New Mexico requires that we use 12.5% of the capacity of the scale to calibrate it. For example, we are required to use a minimum of 625lbs to calibrate a 5,000lb scale.
- Do not use a living creature as a weight to calibrate your scale. Not even your brother‐in‐law. Animals and people move—even when they’re trying not to, and when you’re calibrating the scale, the scale is taking hundreds of readings / second to calculate the conversion from analog to digital. It is not possible for a living creature to stand still enough for the calibration to be accurate. Use feed bags, tractor weights, salt, mineral blocks, bags of quickcrete, etc.
