BPC300-C Photochromic Contact Lens Spectrophotometer
Components and Options
The BPC300-C is a complex system. This page outlines several of the key components and shows what standard options are available.
Monochromators
The spectral transmittance measurements are based upon two Bentham symmetric Czerny-Turner monochromators. These precision devices achieve a wavelength accuracy of ±0.15nm using their 1800nm gratings, and are typically configured for a bandwidth of 5nm. Due to the measurement geometry, the calibration of these devices can be verified in-situ with an optional absorptive standard that can be mounted in the beam path for field-recalibration1.
Features
- Two single Symmetric Czerny-Turner monochromators moving in tandem:
- monochromator 1 acts as a tunable light source, producing a monochromatic probe beam
- monochromator 2 acts as a tunable filter, attenuating the conditioning beam but allowing the probe beam to pass
- 300mm focal length
- 5nm bandwidth (configurable with replacable slits)
- ±0.15nm wavelength accuracy
- up to three gratings per monochromator are possible.
Components
Notes: 1. The accuracy that can be achieved with field-recalibration with an absorptive standard may be lower than factory calibration.
Water Bath
The unit houses a container with apertures for the probe and conditioning beams that allows the sample lenses to be placed in a water bath, both to supply a temperature-controllable medium as well as to reduce the effective optical power of the lenses being measured. An integrating sphere on the output catches light at whatever deviation remains.
Features
- Peltier heated and cooled, 20°C-50°C
- Temperature sensor
- PID temperature control to within ±0.2°C
- Fill funnel, drain valve
- The enclosure has a dry-gas purge capability to prevent fogging of the windows at or below ambient temperature
- Continuous gentle mixing by an immersed impeller to prevent temperature gradients
Carousel
The carousel is a device placed into the water bath to hold and automatically change between 6 samples, a clear aperture, and a lux-measuring photodiode to monitor conditioning beam intensity between sample measurements.
A motorised rotating mount selects the target device, aperture, filter, or the photodiode automatically during the measurement sequence. The other samples are sealed in darkness using metal plates clamped around rubber o-rings when the conditioning beam is active.
Features
- 6 sample positions that can magnetically hold contact lenses or other samples, for example neutral density filters for system validation
- 1 clear position for automatic reference measurement
- 1 photodiode position with photopic sensitivity to allow the automatic characterisation of the conditioning beam
- O-rings and metal plates on either side of the samples not currently being measured allow them to be kept in darkness
Conditioning Source
The conditioning source is based on a Xenon short arc lamp. The UV-rich light of the lamp passes through a rotating wheel that can place 4 customisable and lockable iris aperatures into the beam to attenuate the overall intensity. The attenuated light then passes through a rotating filter wheel, which can hold up to 6 filters to further control the spectrum of the conditioning beam. The light is guided to the water bath by fibre bundle, where it is collimated and shone onto the sample from two directions. Further spectral modulation is possible by partially covering the fibre bundle entrance with another filter. The source also houses a shutter.
The conditioning source is powered by a Bentham 610 Current Stabilised Lamp Power Supply, a high power current source with excellent stability.
Features
- Xenon short arc lamp
- Spectrum controllable with filters and iris apertures
- Nominally matched to AM2
- Shutter
Components
Probe Beam Source
The probe beam originiates from a 250W quartz halogen bulb in a custom enclosure that also houses an optical chopper, and cooling fans. Like the conditioning beam it is powered by a Bentham 610 Current Stabilised Lamp Power Supply, a high power current source with excellent stability. This provides a probe beam powerful enough after monochromation to accurately measure the optical density, but which when spread across several mm2 is sufficiently diffuse to avoid activating the samples.
Components
- ILD-QH-CHOP-24 housing
- 610 Current Stabilised Lamp Power Supply
Acquisition Electronics
The main transmittance measurement acquisition detector of the BPC300-C system is a DH_30_TE Thermoelectrically-Cooled Multi-Alkali Photomultiplier. The signal is recovered from this using a combination Bentham 477 AC current pre-amplifier and Bentham 496 DSP lock-in amplifier, precision acquisition electronics that can boost miniscule currents while discarding the DC signal from the conditioning source.
The photodiode in the carousel is measured using a Bentham 487 Picoammeter for precise determination of the incident beam intensity.
The modules are housed in a 417 detection electronics mainframe, together with auxilliary control modules, such as a Bentham 215 High Voltage Power supply to provide the necessary potential to the photomultiplier, and a Bentham 218M Optical Chopper & Control Module.
Components
Control Software
The BPC300-C is controlled via USB by Bentham's BPC300-C measurement and automation utility Photobench, an add-on to Bentham's popular BenWin+ spectral analysis suite. Photobench controls the BPC300-C hardware, measuring each lens automatically and sequentially by a standards compliant process, or by a process defined by your scientists. Once the measurements are complete, Photobench calculates relevant photometric values for each sample by standards compliant methodology, and presents these to the user as a PDF report or a computer-readable XML file.
The system maintains an audit log, optional user management and a permission system that allows you to create user accounts with restricted permissions depending on user roles independently from your main IT infrastructure, or simply BenWin+'s full set of features available without restrictions.
Features
- Standard USB control, no special computational requirements
- Windows 10 compatible
- Optional user rights management / audit log / XML file production for LIMS support
- powerful spectral and colorimetric analysis features
- photochromic parameters are calculated automatically
- PDF output reports
Options
| Component | Purpose | Code |
| BPC System and Software | Photochromic Contact Lens characterisation | BPC300-C |
| Liquid Calibration Standard and Holder | On-Site recalibration of TMC300 Wavelengths, in-situ | |
| IDR150 System | On-site conditioning beam spectral measurement, immersed, at sample plane. Includes intensity-calibrated light source for absolute measurements. | |
| Emissive Calibration Standard | On-site recalibration of IDR150 System wavelength from atomic emission lines | CAL_CL_HG |
| Deuterium Lamp | Measurements below 280nm | IL6 |
| 706 Power Supply | Deuterium Lamp Power Supply | 706 |
| Alternate diffraction gratings | Allows measurement of extended spectral range | various, contact us with requirements |
| Alternate slit widths | Enables measurements at different bandwidths | various, contact us with requirements |
| Windows-based Control PC | Drives hardware | various, contact us with requirements |
Measurement Process
More details on the measurement and conditioning processes are provided in the Measurement page.