If you already have a VFFS machine, adding a new multihead weigher can look simple: install it above the bagger, connect a few wires, and start production.
In practice, that is where many retrofit projects go wrong.
The machines may run perfectly on their own but produce empty bags, double fills, product in the cross seal, or unexplained stops when connected. A successful retrofit depends on four things: signal logic, cycle timing, the discharge path, and the acceptance test.
The short answer: A multihead weigher can usually be integrated with an existing VFFS machine if both suppliers confirm the electrical handshake, available filling window, chute dimensions, stop logic, and test criteria in advance.
Start with the Existing VFFS, Not the New Weigher
Before choosing the number of heads or hopper size, establish what the current bagger can accept. Its brand and model are helpful, but not enough.
The integration team should collect:
- VFFS brand, model, and year
- Electrical drawings and current I/O list
- PLC type, signal voltage, and available terminals
- Intermittent-motion or continuous-motion operation
- Actual stable speed for each bag format
- Bag dimensions and forming-tube drawings
- Height and position of the product inlet
- Product, piece-size range, target weight, and bulk volume
- Available headroom and platform space
- Plant requirements for guarding, hygiene, and safety
The phrase actual stable speed matters. A bagger rated at 80 bags per minute may run one product at 70 and another at 45. Product size, dust, bag format, and sealing time all affect usable output. Select the weigher against the real production cycle, not the largest number in the brochure.
How Do the Multihead Weigher and VFFS Exchange Signals?
One machine must control the filling sequence. The VFFS often acts as master because it knows when a bag is open and the sealing jaws are clear. This should still be confirmed from its program.
A typical handshake may include the following signals:
| Signal | Typical direction | Purpose |
|---|---|---|
| Weighment ready | Weigher to VFFS | A complete target dose is available |
| Discharge request or bag ready | VFFS to weigher | The bagger is ready to receive product |
| Discharge complete | Weigher to VFFS | The dose has been released |
| Run enable or discharge inhibit | Either direction | Holds production during a stop |
| Machine fault or not ready | Either direction | Prevents the other machine from continuing |
Signal names vary, and not every installation needs all of them. What matters is documenting exactly what each one means.
The details are easy to overlook: Is it a pulse or maintained signal? Which edge activates it? How long must it remain on? Is the contact normally open or closed? If a request arrives before the dose is ready, is it stored or ignored? These decisions often explain why a line passes one test but fails after repeated stops.
Fault behavior matters just as much. If film runs out or a guard is opened, the weigher must not discharge. If the weigher is not ready, the VFFS should wait or stop safely. After reset, both controls must agree whether the earlier request and prepared dose remain valid. Emergency stops and safety interlocks belong in the approved safety system, not ordinary production I/O.
Discharge Timing: Matching the Weigher to the VFFS Cycle
Machine speed alone does not describe the available filling time. One cycle normally looks like this:
- The weigher prepares the target dose.
- The VFFS reaches its filling position.
- The VFFS sends a discharge request.
- The collection or timing hopper opens.
- Product travels through the chute and forming tube.
- The product clears the cross-sealing area.
- The VFFS closes the jaws and starts the next cycle.
The controls must allow for gate-opening, product flight, and settling. Chips, nuts, frozen dumplings, and long pasta do not fall in the same way. A delay that works for 100 g may be too short for 1 kg of the same product.
The weigher also needs capacity above planned line output to recover from normal variation and brief interruptions. Set that margin through trials with the most difficult product and target weight.
Incorrect timing usually leaves visible clues:
| Production symptom | First area to check |
|---|---|
| Empty bag | Missed request or dose not ready |
| Double-filled bag | Repeated or remembered request |
| Product in the cross seal | Flight or settling time too long |
| VFFS waiting every few cycles | Weigher cannot sustain the requested rate |
| Unstable speed after restarting | Reset sequence is not clearly defined |
Chute Design: Getting the Product into the Bag Properly
The chute is not just a stainless-steel connector. It must deliver the complete dose before sealing without breaking product, blocking, or carrying crumbs into the seal.
Consider the weigher outlet, forming-tube inlet, narrowest opening, dose volume, drop height, angle, and offset. Leave clearance for removal and cleaning. A forming-tube drawing is more useful than an outside photograph of the VFFS.
Different products call for different decisions. Fragile snacks benefit from a shorter, smoother fall path. Sticky food needs sufficient angle and no ledges where pieces can collect. Large or long products need a generous opening without sudden reductions. Dusty or heavily seasoned products need a controlled path that helps keep fines away from the sealing jaws.
A timing hopper may help when the bagger has a short filling window, the drop is long, or a prepared dose must be released quickly. It also adds height, another gate, and more surfaces to clean. Use it to solve a measured problem, not automatically.
FAT: What Should Be Tested Before Shipment?
Be clear about what can be proven at the supplier’s factory. If the existing VFFS remains at the customer’s site, a standalone weigher test is not a complete line FAT.
A practical validation plan has three parts:
1. Product FAT
Run representative material through the weigher, including the largest, smallest, and most difficult pieces. Record stable output, weight results, giveaway, damage, sticking, and discharge consistency.
2. Interface Simulation FAT
Use a signal simulator or test PLC to reproduce the VFFS handshake. Test normal, early, held, and repeated requests, plus a bagger stop, weigher alarm, and reset sequence.
3. On-Site Acceptance Test (SAT)
Complete the final test with the real VFFS, forming tube, film, product, and utilities. This confirms actual drop time, sealing clearance, vibration, access, and line recovery.
Acceptance should never be only “the machine runs well.” Agree measurable points: output, weight tolerance, empty or double fills, damage, seal contamination, alarm recovery, and test duration.
The final documentation should include the approved I/O matrix, timing sequence, electrical drawings, chute and layout drawings, FAT results, parameter backup, and any changes made during testing.
What Still Needs to Be Checked During On-Site Installation?
At the customer’s factory, begin with a dry-cycle signal test. Run product slowly, then increase speed in steps. Check the smallest and largest formats, not only one comfortable setting.
The chute must enter the filling path without transferring unwanted force or vibration to the weigher. Operators should be able to remove contact parts, reach the forming tube, and clean between the machines without dismantling half the line.
Once the line is stable, save the final recipes and record a baseline for speed, weight performance, delays, and alarm settings. That record makes later troubleshooting far easier.
Information Needed to Assess Your Existing VFFS
Send Smartpack the VFFS nameplate, manual, electrical drawings, I/O information, forming-tube dimensions, and a cycle video. Add product details, target weights, bag sizes, required speed, available height, and FAT criteria.
With that information, the engineering team can determine whether the project needs a simple hardwired connection or additional PLC work, a timing hopper, a custom chute, or platform changes before the design is finalized.
Frequently Asked Questions
Can a Smartpack multihead weigher connect to any VFFS brand?
It can connect to many brands, but compatibility must be confirmed from the electrical, control, mechanical, and safety information. “Universal connection” should not be promised from the model name alone.
Does the VFFS PLC need to be modified?
Not always. Some baggers already have configurable filler signals. Older or highly customized machines may require program changes or an interface relay panel.
Is a timing hopper always required?
No. It is useful when the filling window is short or the product must be staged close to the bagger. A direct chute may be simpler and easier to clean when the timing already works.
Can FAT be completed without the existing VFFS?
The weigher and simulated signal interface can be tested, but full integration cannot be proven without the actual bagger. Final acceptance should therefore include on-site SAT.
Conclusion: The Small Interface Details Matter
The best integration is not dramatic. The VFFS asks for a dose, the weigher releases it once, the product clears the seal, and both machines recover predictably after a stop. Reaching that point depends less on connecting two familiar machine names and more on resolving the small interface details before installation.