Most packed-food and pharma lines need two end-of-line checks: is the pack the right weight, and is it free of metal? You can buy a check weigher metal detector combo that does both on one frame, or two separate machines placed one after the other. Neither choice is always right. This guide compares them on floor space, cost, flexibility and audit records, and ends with a decision table you can use in a project meeting.
What a combo system is
A combination system mounts a metal detector head and a check weigher on a single frame. Packs pass through the detector aperture, then across the weigh belt, and both results feed one controller.
Three things are shared:
What a combo system is
A combination system mounts a metal detector head and a check weigher on a single frame. Packs pass through the detector aperture, then across the weigh belt, and both results feed one controller.
Three things are shared:
- One conveyor line, so there is one infeed, one set of belts and one transfer point fewer.
- One operator screen (HMI), holding the product recipe for both weight limits and metal-detection settings, so a changeover selects both at once.
- One reject station, usually with separate reject paths or bins so metal rejects and weight rejects can be kept apart.
TCT's Combo Check Weigher with Metal Detector weighs packs from 20 g to 5 kg with published weighing accuracy of ±0.02 g. Its detector head has a 150 mm aperture width and 100–200 mm aperture height. Published test sensitivities without product are 0.8 mm ferrous, 1.0 mm non-ferrous and 1.2 mm stainless steel, with an integrated dual reject, SS
304 build and IP65 rating. Real-world sensitivity always depends on the product, so confirm it on your own packs.
Editor: insert TCT combo unit photo here.
Floor space and integration
Floor space is the most common reason to choose a combo. On a crowded end-of-line, every metre between the sealer and the case packer is valuable.
With two machines you need two infeeds, two sets of belts and usually a transfer gap between them. A detector also needs a metal-free zone around its aperture, so it cannot be pushed tight against the steel frame of the next machine. A combo design builds that spacing in once.
Editor: insert two layout diagrams here. Diagram A: sealer → metal detector (own conveyor + reject) → transfer → check weigher (own conveyor + reject) → case packer. Diagram B: sealer → combo unit (detector head + weigh belt + dual reject) → case packer. Label overall line length on both.
Installation is simpler too. A combo needs one power supply, one air supply, one set of line signals to upstream and downstream equipment, and one commissioning visit. Operators learn one screen.
Cost comparison
Compare total cost of ownership, not just the quotation.
A combo saves money and space, but it ties two quality checks to one mechanical system. If the weigh belt needs maintenance, your metal detection stops too.
When separate machines are better
Separate machines are often the stronger choice in these situations:
Different inspection points. Good practice is to detect metal as early as is useful and again on the finished pack. If your HACCP plan puts metal detection on bulk product before packing (for example, a gravity-feed detector on free-falling powder), a combined end-of-line unit does not replace it.
Very high speeds. At the top end of line speed, a dedicated ultra high speed check weigher or a dedicated detector may outperform a shared frame. Combos are tuned for a balance of both functions.
Large or awkward packs. If your packs are wider or taller than the combo's aperture, or heavier than its weighing range, you need a standalone conveyor metal detector with a larger aperture and a matching check weigher.
Separate validation or ownership. Some sites manage the metal detector as a critical control point owned by food safety, and the check weigher as a quality or legal-metrology device owned by production. Separate machines can make those responsibilities and records cleaner.
Phased investment. If you already own a reliable detector or check weigher, adding the missing one alone may be cheaper than replacing both.
Reject verification and audit records
Whichever layout you choose, auditors will ask how you know that every reject actually left the line, and how you prove each function was checked.
Food safety standards expect this. The BRCGS Global Standard Food Safety Issue 9 requires foreign-body detection equipment to be validated and its effective operation checked at defined frequencies, including the reject mechanism. Issue 10 is in development with a technical working group that began meeting in April 2026, so watch for updated wording.
For a combo system, check these points:
304 build and IP65 rating. Real-world sensitivity always depends on the product, so confirm it on your own packs.
Editor: insert TCT combo unit photo here.
Floor space and integration
Floor space is the most common reason to choose a combo. On a crowded end-of-line, every metre between the sealer and the case packer is valuable.
With two machines you need two infeeds, two sets of belts and usually a transfer gap between them. A detector also needs a metal-free zone around its aperture, so it cannot be pushed tight against the steel frame of the next machine. A combo design builds that spacing in once.
Editor: insert two layout diagrams here. Diagram A: sealer → metal detector (own conveyor + reject) → transfer → check weigher (own conveyor + reject) → case packer. Diagram B: sealer → combo unit (detector head + weigh belt + dual reject) → case packer. Label overall line length on both.
Installation is simpler too. A combo needs one power supply, one air supply, one set of line signals to upstream and downstream equipment, and one commissioning visit. Operators learn one screen.
Cost comparison
Compare total cost of ownership, not just the quotation.
A combo saves money and space, but it ties two quality checks to one mechanical system. If the weigh belt needs maintenance, your metal detection stops too.
When separate machines are better
Separate machines are often the stronger choice in these situations:
Different inspection points. Good practice is to detect metal as early as is useful and again on the finished pack. If your HACCP plan puts metal detection on bulk product before packing (for example, a gravity-feed detector on free-falling powder), a combined end-of-line unit does not replace it.
Very high speeds. At the top end of line speed, a dedicated ultra high speed check weigher or a dedicated detector may outperform a shared frame. Combos are tuned for a balance of both functions.
Large or awkward packs. If your packs are wider or taller than the combo's aperture, or heavier than its weighing range, you need a standalone conveyor metal detector with a larger aperture and a matching check weigher.
Separate validation or ownership. Some sites manage the metal detector as a critical control point owned by food safety, and the check weigher as a quality or legal-metrology device owned by production. Separate machines can make those responsibilities and records cleaner.
Phased investment. If you already own a reliable detector or check weigher, adding the missing one alone may be cheaper than replacing both.
Reject verification and audit records
Whichever layout you choose, auditors will ask how you know that every reject actually left the line, and how you prove each function was checked.
Food safety standards expect this. The BRCGS Global Standard Food Safety Issue 9 requires foreign-body detection equipment to be validated and its effective operation checked at defined frequencies, including the reject mechanism. Issue 10 is in development with a technical working group that began meeting in April 2026, so watch for updated wording.
For a combo system, check these points:
- Separate reject identification. Metal rejects and weight rejects should go to different, lockable bins, or be logged separately, so a metal reject is never mistaken for an underweight pack and reworked.
- Reject confirmation. A sensor after the reject device should confirm the pack left. If confirmation fails, the line should stop.
- Bin-full and door-open alarms. These stop the line before rejects can back up into accepted product.
- Test-piece routines. The HMI should prompt operators to pass ferrous, non-ferrous and stainless test pieces at set intervals, and record the result.
- Weight check records. Batch counts, mean, standard deviation and reject totals per batch.
- Access control. Settings changes restricted by password level. TCT's combo includes a stop-belt reject option, three-tier lamp and audible alarm as standard.
For pharma users, these records also support revised Schedule M and, for US exports, FDA 21 CFR Part 11 expectations. Ask what the software logs and how records are exported.
Request a free line assessment or product trial.
Frequently asked questions
Is a combo less sensitive than a standalone metal detector? Not inherently. Sensitivity depends mainly on aperture size, product effect and the detector electronics. Compare test results on your own product.
Can a combo keep metal and weight rejects separate? Yes, if it has dual reject paths or separately logged rejects. TCT's combo uses an integrated dual reject.
Does a combo need separate validation for each function? Yes. Weighing and metal detection are tested separately even when they share a frame.
Request a free line assessment or product trial.
Frequently asked questions
Is a combo less sensitive than a standalone metal detector? Not inherently. Sensitivity depends mainly on aperture size, product effect and the detector electronics. Compare test results on your own product.
Can a combo keep metal and weight rejects separate? Yes, if it has dual reject paths or separately logged rejects. TCT's combo uses an integrated dual reject.
Does a combo need separate validation for each function? Yes. Weighing and metal detection are tested separately even when they share a frame.