Most plastic that has to block light carries an opacity requirement that gets verified in a lab, on a coupon, after the run. That works for qualifying a formulation. It leaves everything produced between coupons unverified, which is a problem when the failure mode is a pharmaceutical bottle that lets light through and a product that degrades on a shelf months later.
Measuring it on the line closes that gap, and the OPAX-1000 opacity and turbidity sensor is built to do it at production speed. This guide covers what the reading represents, the geometry that has to be right before anything else, how to calibrate against your own material, how to set the outputs so a PLC actually captures them, and the applications where you should specify a different instrument.
What the Reading Represents
The OPAX-1000 is a transmitter and receiver pair. The transmitter directs a modulated 880 nm infrared beam through the sample, and the receiver measures the diffused light that arrives. Two seven-segment digits report that as a relative value from 00 to 99.
Modulating the source is what makes the measurement usable on a plant floor. The receiver responds to the transmitter’s signature rather than to whatever ambient light is falling on the line, so overhead lighting and seasonal daylight do not move the number.
The value is relative to your own reference. It is a comparison against material you have taught the sensor to treat as acceptable, which is what an inline gate needs. A laboratory figure for a specification sheet or a certificate is a different measurement made on a different class of instrument. Decide which one your requirement calls for before you mount anything, because the sensor will answer the first question well and cannot answer the second.
Set the Geometry Before Anything Else
Transmitter-to-receiver spacing runs 50 mm to 200 mm. That single number decides more installs than any other spec on the sheet, and it is worth checking against your line before the specification goes further.
Within that span, position matters:
- Measure through the center of the target. Edges and curvature scatter light in ways that will not repeat.
- Keep the sensor and light source 1 cm to 2.5 cm from the surface as it passes through the beam. Standing off further lets adjacent containers scatter light into the receiver and contaminate the reading.
- Mount both halves rigidly. Alignment drift reads as an opacity change, and the sensor has no way to tell the difference. The OPAX-1000B bracket carries the transmitter, the receiver, and a position sensor together, with the transmitter adjustable along the top rail so spacing can be set once and locked.
The sensitive area is an 18 mm lens, so what you get is a point measurement at one location. That is the right instrument for a bottle, a tube, or a fixed track on a web. It is not a full-width scan.
Calibrate Against Your Own Material
The sensor ships with defaults that will not match your resin. Three steps get it onto your material.
Choose the LED intensity. Three levels are available, shown on the display as U1, U2, and U3 for low, medium, and high. The default is U2. Thin or lightly filled material usually calls for a lower setting, because a source that overpowers the sample flattens the difference between a good part and a bad one.
Null the sensor. Block the light from the transmitter and hold the T/+ key until the sensor zeroes. The display flashes the value being subtracted.
Set the reading. With a known-good target in the beam, a short press of either key enters adjustment mode, and T/+ and P/- move the displayed value to where you want your reference to sit.
Pro Tip: Null the sensor every time you change LED intensity. Skipping that step is the most common reason a carefully calibrated reading drifts after someone adjusts the source, and it takes about 10 seconds.
Build your reference from a spread of real production, not from one good part. Opacity in a filled plastic tracks pigment loading directly, and the OPAX manual includes a curve of relative transmission against titanium dioxide let-down ratio in HDPE to make the point. A let-down change, a resin change, or a thickness change moves your baseline, so the reference has to come from the material you are actually running.
Dive Deeper: EMX’s engineers worked through this on a customer’s filled film and published the parameters they landed on, including the 150 mm spacing and the aperture they added to cut source intensity. See Verifying Opacity in Plastic Film.
Set the Outputs So the PLC Catches Them
The discrete output changes state when the measured level reaches the threshold you set. Default threshold is 15, and the output is selectable normally open or normally closed, so you can put the trip on whichever condition your logic treats as the fault.
Three settings around it are worth deliberate choices:
Hysteresis runs H0 through H9, default 2. It sets how far the signal has to move back past the threshold before the output releases. For example, with a threshold of 25 and hysteresis of 4, the signal has to fall to 20 before the sensor un-detects. Without it, material that hovers at the trip point chatters the output.
The extended output pulse runs P0 through P9, adding 0 to 90 ms in 10 ms increments. The sensor can respond in the 25 microsecond range, which is faster than most PLC scan rates. If the controller is missing events that the display clearly shows, this is the setting to reach for before anything else.
The analog output is 0 to 5V at 20 mV resolution. Use it when a pass/fail bit is not enough, such as watching a gradual drift in pigment dispersion across a roll rather than waiting for parts to cross the reject line.
Two more worth knowing. A LASER-MARK position sensor can tell the PLC when a sample is actually in position, so readings taken between containers are not treated as data. And the sensor locks two ways: local lock from the keypad, or remote lock by tying the yellow conductor on the M12 connector to supply voltage, which keeps settings intact after commissioning.
Configuration is ordered as separate halves, the OPAX-1000R receiver and the OPAX-1000T transmitter, with the bracket, position sensor, and cable as accessories. Where the material transmits more light than the standard source can resolve against, such as PET bottles, the OPAX-1000-THP high-power light source is the variant to ask about.
Where the OPAX-1000 Is the Wrong Choice
Four limits worth confirming before you specify it.
It is not rated for pressure washdown. The housing is IP65, and EMX states the washdown exclusion directly. On a line that gets hosed at shift change, the mounting position has to account for that.
It reports relative transmission, not a laboratory value. If your requirement is a number on a certificate of analysis, that comes from a bench instrument, and the OPAX-1000 sits alongside it as the inline gate rather than replacing it.
It measures one spot. With an 18 mm lens and a 200 mm maximum span, a wide web needs multiple heads at fixed positions or a different approach entirely.
Operating temperature is -20°C to 55°C. That covers most of a converting hall and is worth checking near a die or an oven.
One adjacent case: if what you actually need to know is the color of a translucent material rather than how much light passes through it, that is a transmitted color measurement and the ColorMax VIEW is the sensor for it.
Test It on Your Own Resin First
Every number above is a starting point. Filler package, thickness, line speed, and web flutter all shift where the threshold should sit, and no data sheet predicts that combination.
EMX will run free sample testing on your actual material. Send in the film, sheet, or container, and the matching sensors get tested in a real-world setup with a report on what each read and what to change at integration. Send us a sample and get the spacing, intensity, and threshold settled with data before the sensor goes on the line.
