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High Precision Weigh Terminal Case Study

Mettler Toledo's High Precision APW Weigh Module with High Throughput to PLC

The Problem

Cech recently had a customer reach out to us regarding a concept to capture the weight of an automotive part for one of The Big Three. Some of the issues included concerns about cycle time, the ability to communicate with a high-clocked PLC, and the ability for the weigh module to provide a stable and accurate weight.

The cycle time for this station was going to be approximately four seconds. It would start from the time the part is placed on the weigh module via a robot arm to the time that the part is picked up and removed. The part would then either be accepted or rejected and placed on the appropriate conveyor. The weight of the part was extremely light, around 285 grams. It had a tight tolerance - plus or minus no more than half a gram.

The Solution

We arranged for a product demonstration at the customer's site, with approximately 50 of the parts that they were wanting to weigh. The product we used for the demonstration was a Mettler Toledo WMS High Precision Weigh Module. This weigh module was communicating to a Mettler Toledo ACT350 Precision Din Rail Terminal.

We went through and verified the part weight variance of each of the 50 parts. After some refinements were made, we were able to determine that we had the capability to accurately decipher a good part from a bad part within the tolerances given. Once we completed the demonstration, the customer moved forward with a formal quote for their specific application.

We provided the customer with the following solution:

A Mettler Toledo WMS6002C-L/01 weigh module with a 6,200 g capacity and a readability of 0.01 g. It has a rugged industrial design and it offers overload protection. The stabilization time for this unit is 0.8 seconds with 92 updates per second. This far exceeded the minimal requirements for this application.

We used a five-meter WMS connection cable with an open end to connect to a Mettler Toledo ACT350 precision terminal that was din rail mounted into the customer's control panel. The ACT350 allowed for a Profinet connection to the PLC and configuration from a web server connection to a PC. The ACT350 has a simple-to-use front display with keypad and status LEDs. This unit supports a quick cycling PLC.

In addition, we also supplied a Mettler Toledo WMS Weigh Module Weighing Pan. It was 58 mm X 58 mm, which allowed the customer to build a nesting fixture to the top of the weigh module.


We had a total project cost of approximately $12,500. This included the equipment itself, along with the calibration of the equipment, and delivery to the site.

The Payback

The return on investment (ROI) was almost immediate since they were only visually inspecting parts beforehand. This caused them to have many rejected parts with a chargeback. This also eliminated human error by using a system based on weight as apposed to visual inspection by a person.

This system increases productivity by allowing the operator to perform other task which also contributed to the return on investment.

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