More and more people are opting out of using a speed sensor because they think that their belt conveyor runs the same speed all the time. The popular assumption is that not having a speed sensor saves them money, but does it really?
Let’s work through a typical example. Conveyor belts incorporating a weighing system utilize some type of integrator for data processing.
The integrator works on a belt scale as follows: Load X Speed = Rate. So if your speed is off, your rate is off.
For example: if your belt is off by 1 to 2 feet per minute (FPM), over time this could make your rate totals off by 1 or 2 percent, or even more.
Why doesn’t a belt scale run at a constant speed?
If you were to put a speed sensor on the conveyor, you would see that no belt runs the same speed.
The reason why a belt does not run at constant speed is usually due to the difference in the amount of material on the belt and the load on the conveyor motor. For example, a belt conveyor with no load or product on the belt can run at 200 FPM, but when the belt is loaded it may only run at 198 FPM. Similarly, the belt length can also be a factor. The longer the belt, the more load is on the motor and that could change the speed. The belt’s start up/shut down process can also attribute to inconsistent speeds. During these periods, there is a speed-up time or a speed lost that may affect the outcome of the rate in totals.
After installing many belt scales and conveyors, I have found that all belts vary in speed. I have seen the speed change as high as 5 FPM.
It’s important to have a speed sensor in your system because they are built to know when the belt slips or brakes on the conveyor. Siemens integrators have relays that can be set to active at when this occurs. Based on the example above, even a 1 or 2% rate change would compensate for the cost of a speed sensor.
What issues have you experienced by not including a speed sensor in your process?