What is the minimum time needed for check weighing using a HI 1756WS?

There are many factors that determine the time it takes to make a final weight reading. The HI 1756WS updates (reads and makes available) the load cell data every 20ms. This can be an empty scale, a scale in transition, or a fully loaded scale.

When a weight is placed on the scale the HI 1756WS begins reading the weight as soon as the load cell starts to deflect. This deflection of the load cell determines the weight controller reading. The length of time needed for the load cell to deflect would be a determining factor in any delay in the update.  If the load cells could deflect the full weight change on the scale within the 20ms, then with the next update all the information needed to take a weight measurement would be available.

There are other factors that extend the time to take a weight reading, including in-plant and process vibration. Use the WAVERSAVER® settings that minimize the effect of in plant and process vibration. The WAVERSAVER® setting will affect the weight measurement time. The lower the frequency of vibration, the longer it takes to calculate the real weight reading. WAVERSAVER® settings and time required are 7.5hz=75ms, 3.5hz=150ms, 1.0hz=600ms, 0.5hz=1.2sec, 0.025=2.5sec.

Averaging is used to smooth out material impacting. Each average extends your time 20ms.

Then there is the time it takes the load cell to realize the full load of the product being weighed. The physical deflection and stabilization is critical and a fast time is considered as just under 100ms.

The amount of time it take for a single product to be fully on the scale should be considered.

There would need to a be a timing calculation or indication to the computer to tell the computer when to take the weight reading.

You have scan time delays on the back plane. This would have a minimal affect on the weigh time, but may need to be considered.

With these considerations you can calculate the minimum amount of time it takes to read a weight.

An example would be to run 200 cans per minute. This give you 300ms per can. This 300ms is to get the can onto the scale, settle, and get off the scale. With WS=7.5hz, averages=1, 100ms scale settling, plus one scan. The can must be on the scale for 215ms, minimum. With 300ms you have to include can approach and exit time. So it would be a close application. Fast settling times on the scale, and the can approach and exit times will make or break this application.