Sensors for Packaging and Pharmaceutical Machinery

Packaging and pharmaceutical machinery asks sensors to do the two things they find hardest — detect transparent and low-contrast material, and do it fast — while surviving frequent format changeovers and, in pharma, a cleaning regime with documentation attached.

Here is how the specification usually needs to go.

Transparent material is the defining problem

Clear film, PET bottles, glass vials, blister foil backing and cellophane overwrap are all close to invisible to a diffuse photoelectric sensor. The light passes through, very little comes back, and detection is marginal in a way that varies with ambient light and film tension.

The reliable answer is through-beam. Emitter and receiver facing each other, the target detected by beam interruption rather than reflection. Even a transparent object attenuates the beam measurably, and with sensitivity set correctly this is stable where diffuse sensing is not.

Where a through-beam arrangement is not mechanically possible, retro-reflective is second best, but expect to spend commissioning time on sensitivity and expect it to need revisiting when the film supplier changes. The D31C range covers all three modes in M18 and M30.

Speed, and what it means for switching frequency

A packaging line running 300 packs a minute gives a sensor 200 milliseconds per pack, and the detection window inside that is much shorter. Two things have to be fast enough: the sensor, and the controller reading it.

Switching frequency is a specification parameter that gets ignored on slow applications and becomes decisive here. If the sensor is counting, specify against the maximum line rate with margin, not the nominal rate.

The failure mode is characteristic: counts that are correct at low speed and drift low as the line speeds up. If you are seeing that, the sensor or the input scan rate is the cause, not the mechanism.

Small targets and tight geometry

Packaging machinery is compact. There is rarely room for an M30 body, and the targets — a tablet, a cap, a label edge — are small. This pushes towards M8 and M12 inductive bodies for metal targets, and towards photoelectric with a well-defined beam for everything else.

Where the target is small relative to the sensing field, the sensor may respond weakly or inconsistently. Specify the target size when you enquire; it changes the recommendation more than people expect.

Changeover survives or it does not

A line that changes format several times a week puts mechanical stress on everything adjustable. Sensors get knocked, brackets get moved and not moved back, and cables get caught.

Three things help:

• Mount out of the changeover path wherever the geometry allows. The best protection is not being in the way.
• Use positive mechanical location — a dowel or a machined seat rather than a slot — so a sensor that is removed goes back in exactly the same place.
• Specify connector versions rather than fixed cable where sensors are routinely removed. An M12 connector survives repeated disconnection; a cable that is pulled through a machine frame every changeover does not.

Hygiene and cleaning in pharma

On pharmaceutical lines the cleaning regime is validated, which means it will not be adjusted to suit a sensor. Specify to survive it as it is.

• Stainless steel bodies, flush mounting, no crevices, no exposed threads collecting product, no horizontal ledges.
• Chemical compatibility with the actual cleaning agent — including the cable sheath, which is the component most often overlooked and quite often the first to degrade.
• Rating against the wash, not the process. Where high-pressure hot washdown is used, see IP69K washdown specification. The connector matters as much as the sensor: an IP69K sensor on an IP65 connector is an IP65 installation.
• Cable entries pointing down. Standing water on an upward-facing gland defeats any rating eventually.

Documentation

Pharmaceutical and export machinery frequently needs component documentation as part of the machine file — declarations of conformity, material certificates, and in some cases traceability to a production batch.

Establish what your quality system requires before ordering rather than during qualification. Components bought through unofficial channels are commonly untraceable, which is a difficult thing to discover late. Our note on buying direct versus through a channel covers how to avoid that.

Typical sensor map on a packaging line

• Product presence and gap detection — through-beam photoelectric, dark-on
• Counting — photoelectric with switching frequency specified against maximum line speed
• Metal cap, can and foil detection — D30C inductive in M8 or M12
• Carton, plastic and non-metal detection — capacitive, or photoelectric where the target moves fast
• Guard and interlock positions — normally closed, so a cut cable stops the machine
• Format part identification — inductive presence sensing to confirm the right tooling is fitted, which prevents an entire class of changeover error
• Servo and axis position feedback — position measurement rather than switching; see the Novotechnik linear range

Specifying

Send us the target — material, size, whether it is transparent or reflective — the line speed in units per minute, the available mounting space, the cleaning regime, and the output your controller expects. For transparent targets, a sample or a photograph is worth more than a description.