Checking in on Checkweighers

With the increase in regulations and safety concerns, pharmaceutical companies are investing in inspection equipment to ensure the quality of their products.

Kassandra Kania


Although checkweighers are often introduced at the end of the packaging line, they are no longer an afterthought. “[Today’s manufacturers] consider inspection equipment to be an essential part of the quality control process,” says Mark D’Onofrio, vice president at Lock Inspection Systems (Fitchburg, MA). 

Installing a checkweigher yields many benefits. “The checkweigher ensures compliance with label claims and weighing legislation,” he says. “It validates pack weights and checks count of packaged components or insertion of requisite user literature. It also acts as a process control tool, rejecting both under- and overweight packs.” 

Manufacturers of checkweighers and other inspection equipment are developing features that streamline operations and improve accuracy. Customers are also looking to create an audit trail to verify product quality. Equipment suppliers are providing them with checkweighers that help them perform this function. 


A significant change in the pharmaceutical industry has been the introduction of 21 CFR Part 11. This has had an impact on checkweighers, says John Craig, global marketing manager for Thermo Electron Corp. (Waltham, MA). Craig admits that introducing compliance was a challenge as Part 11 is not an equipment requirement. 

However, “we realized that there was an opportunity for us to make checkweighers compliant with electronic signatures,” says Craig. If customers want to change a product setting, recalibrate the checkweigher, or clear an alarm, they have to log onto the machine using a unique user ID and password. “We’re getting a great deal of interest in this,” says Craig. Customers can purchase new checkweighers that are 21 CFR Part 11 compliant. They can also purchase an upgrade kit for their existing machinery, explains Craig. 

Conveying Accuracy

When buying a checkweigher, customers should consider whether the system meets their need for speed and accuracy. “Be very careful,” warns Craig. “People will quote you accuracy, but accuracy isn’t something you can quote without also taking into consideration the weight, shape, and speed of the pack.” 

Certain packages present challenges to the checkweigher, says D’Onofrio. “Bottles and jars, for example, are difficult packs to handle at high speeds. So are polyethylene bags, particularly if they are coming off the bagger at irregular intervals,” he says. Checkweigher manufacturers offer systems to overcome these problems. Lock, for example, makes machines with belt or chain transports and screw feeders or side-belt transfer mechanisms. “This enables the most challenging packs to run efficiently,” says D’Onofrio.

Alan Vaught advises customers to provide a stable and reliable transfer point between their existing or new conveyors and the checkweigher. Vaught is vice president of operations for Thompson Scale Co. (Houston). “A smooth transition of product onto and off the scale is paramount to repeatable and accurate weight,” he says. “We’ve come across many applications where that’s not properly done. Customers are concerned about performance of their checkweighers when in fact there is nothing wrong with the scale. The problem is the product bouncing and bumping as it goes onto the scale.”

Timothy Warren, sales manager, OCS Checkweighers Inc. (Snellville, GA), also notes the importance of having a smooth transfer of product from the infeed conveyor onto the weigh conveyor, and from the weigh conveyor onto the discharge conveyor. “Weighing the product is rarely the challenge,” he says. “The challenge is handling the product.”

The company manufactures its own conveyors. It also balances its rollers to reduce vibration, ensuring greater accuracy. The HC series of checkweighers is designed specifically for the pharmaceutical industry. Conveyors have a 5-mm roller diameter for smooth transition of product. 
For unstable containers that are difficult to run on traditional conveyor belts, customers may want to buy a rotary checkweigher. “The Model HC-IS rotary checkweigher is specifically designed to run tentatively unstable containers that would fall over on a checkweigher that uses three conveyor belts,” says Warren. It also addresses product spacing problems for infeed to the checkweigher. The most significant feature, says Warren, is that the Model HC-IS can be installed at any given point along the production line without cutting or breaking the existing conveyor. “The HC-IS rolls over the top of the existing conveyor,” he explains. “This is significant in applications using an existing product line.”


An important feature of any checkweigher is its ability to detect and reject substandard packages. Thermo Electron Corp. has added extra features to its checkweighers, such as open-flap detection for cartons and fail-safe reject mechanisms. “Normally, with a reject mechanism on a checkweigher, when the machine detects a substandard package, it will reject it,” says Craig. “The fail-safe reject mechanism does the exact opposite. It rejects every package, unless it detects something that gives it reason to accept it. This is tied in with reject validation. We have sensors in the locked reject bin so that when a package is rejected, we expect the sensor to detect a rejected pack going into the reject bin at a particular point in time.”

Thompson Scale Co. has developed a method to automatically detect and reject empty packages. “This comes into play when you consider pills in a blister pack,” says Vaught. “When that low-profile package goes across the scale, many of the checkweighers on the market can’t detect the empty blisters. We are able to give customers 100% assurance by weight that every package is correct.”


Some companies are adding features or combining checkweighers with other systems to customize machines. Thompson Scale Co. has developed a tandem checkweigher. The system uses two different weigh tables to weigh various product sizes. “One customer is using the tandem checkweigher to weigh a tube of ointment that is four inches long. It runs at a rate of 150 products a minute,” says Vaught. “On the same production line, the customer has a larger tube that measures about 10 inches in length. Most people would run the conveyor at variable speeds, using a weigh table that’s long enough to weigh the largest package. The problem is that when you start weighing the smaller package that has closer center-to-center distances, each package is closer together. As a result, you have to run the conveyor at an extremely high rate of speed to be able to run that same package across a longer weigh table.” To solve the problem, Thompson installed two weigh tables in the same checkweigh system—one for weighing the small package and one for weighing the large package. The operator uses a switch to select the appropriate weigh table. He can run the system at a slow, controllable speed and still weigh both the long and the short package. 

Some pharmaceutical companies are integrating a combination system into the production line. Lock Inspection Systems’ WeighCheck Combi combines a checkweigher and a metal detector. The system screens out under- and overweight product as well as product containing tiny metallic particles. “By performing multiple functions, the WeighCheck Combi offers numerous user benefits over separately controlled machines,” says D’Onofrio. “It facilitates operability as well as saving valuable time, space, and resources.” The metal detector is controlled via the checkweigher’s user interface. This allows event reports for both the checkweigher and the detector to be displayed on one large screen. Also, both instruments can be accessed through one touch screen panel.

When making the decision to purchase a checkweigher, customers should not overlook the importance of education. “The buyer must have an appreciation and understanding of the weigh-cell technology and the material-handling characteristics of the checkweigher,” says Warren. They should also give careful consideration to future needs, not just present-day requirements, says Craig. This will help ensure that their checkweigher has the flexibility to handle changing production needs. 

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