What Are Colour, Label and Fork Sensors? Special-Purpose Sensor Selection
Special-purpose sensors are made for a specific job: detecting the colour mark on packaging film, a transparent label, or metal passing through a fork gap.
Special-purpose sensors are made for a specific detection job that general-purpose proximity and photoelectric sensors struggle with. This group includes the colour mark sensor, which reads the printed colour mark (cut mark) on packaging film; the label sensor, which distinguishes transparent labels on a backing tape; and the fork-type inductive sensor, which detects a metal part passing through its fork gap. They are used on packaging, filling, labelling and printing machines for cutting, stopping and positioning signals.
Sensors in the catalog
| Model | Function | Output | Information in the product data |
|---|---|---|---|
| Isıso CMM15-B80-A0 | Colour mark sensor | NPN, NO+NC | B80 housing, coaxial detection, red/green/blue/white light selectable, cable |
| Isıso CMM15-B80-A2 | Colour mark sensor | PNP, NO+NC | B80 housing, coaxial detection, red/green/blue/white light selectable, cable |
| Isıso IPUD-050NP | Transparent label sensor | NPN/PNP, NO+NC | 0.5–2 mm gap, potentiometer adjustment, 2 m cable, −10…+60 °C |
| Isıso IEU55-DS7B | Fork-type inductive sensor | See datasheet | 10–30 V DC, cable |
Selection criteria
- Target: A colour mark sensor for printed colour marks, a label sensor for transparent labels or label gaps, and a fork-type inductive sensor for metal parts or gear teeth.
- Light colour and contrast: On a colour mark sensor, the light colour is chosen to give the highest contrast between mark and background; the CMM15 models in the catalog offer four selectable light colours. Leaving the light on a colour that gives no contrast causes marks to be missed.
- Output type: If the PLC input is sink type (takes a PNP sensor), choose a PNP output; if it is source type (takes an NPN sensor), choose NPN. The CMM15-B80-A0 has an NPN output and the A2 a PNP output; the IPUD-050NP is listed as NPN/PNP in its name.
- Speed: On a fast-moving web, the sensor's response time must be shorter than the time the mark takes to pass the sensor. Take the response time from the datasheet; on a fast web the signal may need to go to a high-speed input module.
- Mounting distance and setup: The colour sensor is mounted at the detection distance and mounting angle given in the datasheet; if the distance changes on a vibrating web, detection fails. The IPUD-050NP is adjusted with a potentiometer.
Common mistakes
- Ignoring the mounting angle on glossy film: On some surfaces glossy reflection misleads the sensor; apply the mounting angle in the datasheet.
- Not re-adjusting on product changeover: On new film the mark and background colours change and the sensor misses.
- Not checking NPN/PNP matching: The input never detects or appears permanently active.
Special-purpose sensors at Welibaba
The Special-Purpose Sensors category has 4 active products from Isıso, all listed with prices: CMM15-B80-A0, CMM15-B80-A2, IPUD-050NP and IEU55-DS7B. General-purpose sensors are in the Photoelectric Sensors and Inductive Sensors categories, and sensor types are explained in the industrial sensor guide.
Frequently asked questions
What does a colour mark sensor do?
It detects the cut mark printed on packaging film; the machine uses this signal to cut or stop the film at the same point every time.
Why is a transparent label not detected by a normal photoelectric sensor?
The difference in light transmission between a transparent label and the backing tape is very small, so a normal photoelectric sensor cannot tell them apart. A transparent label sensor is made for this job.
Where is a fork-type inductive sensor used?
To detect a metal part, gear tooth or metal flag passing through its fork gap, for position and speed detection.