Why the double-feed, or ‘piggyback’ is so costly — and what your scanner does to help stop it
It doesn’t happen often, but when it does, it’s one of the worst – and costliest – mistakes that can happen inside a bank branch, making a check deposit seemingly vanish into thin air. But there’s no magic or sleight of hand involved here. We’re talking about the double-feed, the rock in the shoe of every teller or branch manager who’s been around long enough to see one.
What happens in a double-feed is pretty simple: You have a stack of checks feeding through your scanner, and suddenly two go through at the same time. If you’re lucky, it causes an error and the machine stops as if it was a paper jam, and you get a chance to do it over. But if you’re unlucky, the pair of stuck-together checks zips through undetected, and you get an image of the front side of one check and the back side of the other. Considering what’s printed on the rear of a check (nothing), that means the check that’s in back effectively disappears from the queue, but the machine keeps running without missing a beat.
Naturally, the kinds of problems created by a missing check are ones that you don’t want, well, ever. Someone’s missing their money, and you don’t find out about it until you’ve got an angry customer. By then, the original paper check has probably been filed away somewhere, and you have to hunt for it. And then it has to be re-submitted for the clearing process, likely racking up extra fees. In other words, you’d much rather have it end up as a simple misfeed than the dreaded “piggyback.”
There are a few ways that we try to prevent this. The first is with a rubber part called the discriminator, or separator, that’s right up against the feed rollers at the start of the paper track. The separator’s job is to apply just enough opposing pressure so that only one check at a time can be pulled off the top of the stack. And for the most part, that works fine. The only trouble is that after thousands and thousands of documents are scanned, the friction starts to wear the rubber smooth, and tiny paper particles and ink rub-off also get mashed into it. At that point, the separator is starting to get worn out, and sometimes a second check will slip by. So, making sure the separator is clean and turned to a fresh side is probably the number one way to prevent a double-feed, and we’ve put out many, many support articles and videos stressing that you should stay on top of this.
Left: The discriminator, or separator, is a rubber piece that prevents more than one check at a time from entering the feeder. Right: A separator that is starting to get worn, and should soon be rotated or replaced.
But what happens when you DO have a worn-out separator, or when there’s a different problem that’s beyond your control? If you’ve seen the way some people treat things, it should come as no surprise that a small but non-zero percentage of checks will have something sticky on them. Sometimes, it’s even possible for static electricity to make checks stick to each other.
In those cases, we want a failsafe that will stop the machine if it sees a double-feed get through. And that’s the job of this tiny 10-cent diode that you see in the picture on the right. This is an infrared LED that sends a beam of light across the paper track inside the scanner. Similar to the infrared beams in your garage door opener, or the ones that sound a chime when you walk through the entrance to a store, it shines at a constant rate and then detects when the beam is broken by something – in this case, a piece of paper moving through the scanner.
If the infrared beam is covered up for too long, it probably means that something longer than a standard check has just gone through – most likely two checks stuck together – and it’ll trigger a mechanical stop. The beam is also just intense enough that a normal check doesn’t block it entirely; some of the infrared light still makes it through the paper to the other side. But if two checks pass through at once, they’ll cover up enough light that it falls out of the acceptable range and stops the motors.
Left: An infrared LED that’s a little smaller in diameter than a pencil eraser shines a beam of light that detects double-feeds. Right: The location of the double-feed sensor in the feeder of the TellerScan TS240, which feeds from the left.
On the flip side, while you don’t want a double-feed making it through, you also don’t want the scanner stopping at the drop of a hat, and that’s why we have a system called “Double Feed No Stop,” which uses additional data from the main image sensors, MICR head, and other track sensors to make a more accurate determination about whether you’ve got two checks going through the feeder, or just one!
One final word about double-feeds: The last line of defense against them isn’t a scanner component or a software algorithm – it’s you. One thing about double-feeds is that they’re much more likely to go unnoticed in a large batch of checks than a small one. And so banks that use teller capture – that is, having the teller scan checks immediately with the deposit – have much lower rates of double-feeds than ones that scan them in bulk at set times throughout the day, known as branch capture or back-counter capture. Since the majority of teller deposits have six checks or fewer, that’s an opportunity to nip piggybacks in the bud.
Another, related tool that many banks and credit unions use is called control totals. What that means is that the number of checks in a deposit is counted and entered into the system first, and then they’re fed into the scanner. If the number of checks scanned is different from the control total entered at the start, the deposit is flagged to do over. Again – this is much simpler to do with small batches of checks than large ones, so that’s another advantage for teller capture.
We hope you’ve found this to be an interesting lesson about double-feeds and the steps we take to prevent them – and what you can do to look out for them yourself. If you have any questions or you’d like to know how to get our industry-leading double-feed detection in your branches, contact us and someone will be in touch with you shortly. Thanks for reading, and we’ll see you next time!
