How To..
Make a simple system.
Just plug one of our load cells into our Handheld Display and away you go! The Handheld Display provides power to the load cell and then displays the output in whatever units you’ve set it up in. Simple and portable – Job done!
Control Switching
If you’re looking to act on the values you see, like switch off a pump, set off an alarm or flash a warning light, then we can supply the following:
Our Amp1 ‘All-in-One’ Instrument has optional relays and set points. This allows you to type in two values at which relays will be activated. The relays can be configured to work in multiple ways (momentary, latching, inverted, etc).
Wireless System – Use a wireless transmitter on the load cell (or load cells) and switch equipment with our wireless relay box. The relay box can be easily configured to work with up to 16 load cells. It can switch on individual load cell values, the sum of multiple load cells or the difference between load cells.
Connect Platforms, Silos and Multiple load cell systems
Simple analogue system
The easiest, and cheapest way to measure a load over several load cells, is to connect them altogether in parallel. The resulting signal is then the electrical average of all the units. This method works for most systems where the load is measured in roughly the same position and you’re not looking for very high precision. There are a few points associated with this method which you should be aware of.
- Corner errors – This happens if any of the load cells have a different output (sensitivity). Some manufacturers rationalise their load cells to a specific output (eg 2.00mV/V @ full load) but others only specify a nominal output (eg 2.0mV/V nominal can be anything between 1.80-2.20mV/V). If you have four load cells under a platform with different outputs, and you move your load into one corner, over one particular load cell, then the output from that cell will dominate. If your system was calibrated with the load in the centre, using the average signal, then if this cell has a higher output than the average, you’ll get a slightly higher reading. This is not an issue if you always measure the load near the centre of the platform. This is also not an issue if the load cells are under a silo which contains a liquid, or a self-levelling compound, as the centre of gravity is always in the same place.
- Amplifiers – Amplifiers that also provide power to the load cells will only be rated for a maximum current. This means there will be a limit on the number of load cells the amplifier can drive. All our amplifiers will happily drive at least four 350 Ohm load cells.
- Common Mode – This occurs when the load cells are not electrically balanced. In reality, if you’re using load cells from the same manufacturer (always a good idea), this shouldn’t be an issue.
- Save money – Don’t buy all your load cells with output modules on (eg 4-20mA, 0-5V, etc..). Buy the basic load cells with mV outputs and then use one amplifier (like our Universal Load Cell Amplifier, which has switchable outputs 0-5V, 0-10V, +-10V, 4-20mA). The amplifier case can then double up as your junction box.
Amp3 Universal Amplifier with 3 load cells connected in parallel.
High accuracy analogue system
For higher accuracy systems we would recommend connecting the load cells to an active junction box. This box enables all the load cell outputs to be matched, and eliminates all the electrical interplay between them. This means the output from the active junction is a purely summed signal.
Digital USB system
We can supply our load cells with in-line PC-USB modules, or you can retrofit our PC-USB adaptor to an old load cell. These modules convert the analogue signal into digital data. The digital data can then be read directly into a PC, Laptop or Tablet (running Windows). If you don’t have enough USB ports on your PC you can connect them via a USB hub. The free USB software* can display and log any (or all) of the following in real time:-
- Individual load cells values.
- Multiple load cells values.
- Combined values (load cell A + load cell B – load cell C….etc)
- Mathematically modified values (eg load cell A*2.204 – numerous other mathematical functions available)
Digital Wireless system
We can also supply our load cells with wireless transmitters. By using a PC-USB receiver (Wireless USB PC receiver (500m) ) and the free wireless software you can display and log values as in the wired USB software. The free wireless software ** also allows you to place display boxes on a representation (JPG, GIF, PDF and DXF) of your system, so making visualisation easier. There are also a number of other modules that can “listen in” and use the transmitted data to display, switch or generate an analogue output (0-5V, 0-10V, +-5V, +-10V, 4-20mA).
* Free USB software has a limit of 24 channels. USB hubs need to be powered versions as they supply the load cell with power.
** Free Wireless software has a limit of 100 Channels.
Coming soon!
- How to choose the right capacity of load cell
- How to choose the right accuracy level
