UV-meter design ideas
Early ideas
This page describes the early ideas on how to design the LUVI UV-meter.
The information on this page is partially outdated, but may be helpful to see the design choices that have been made and the different issues that have been looked at when making the design.
The final design is described at
Introduction
This is a simple design for a handheld wideband UV-meter.
It uses as much as possible ready-made components and will need a
minimum amount of soldering.
It fully complies to the requirements, but will only need a sticker over
the rightmost digit to show in mMED/hr.
Components
Box
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45 Series - Design choice
- 117.5 mm x 72.5 mm x 25.5 mm
- Integrated 9V battery compartment with clip
- Silicon rubber boot as option
- CHH451PBK Textured lid - Farnell
- CHH456PBK Recessed lid (for a label) - Farnell
- CHH451BBK - 45 Series rubber boot, Size 1, Black
- CHH451BBL - 45 Series rubber boot, Size 1, Blue - Farnell
-
62 Series - not baseline, interesting for miniaturisation
-
-
Serpac M6
- 105.41 mm x 60.96 mm x 21.59 mm
- Integrated 9V battery compartment with contacts
- Can be customised with full colour printing
- Arrow (black)
- Mouser (all) (black)
-
- BOS 400 with compartment for 9V battery
- 100 mm x 65 mm x 24 mm
- Alternatively BOS 500
series
(120 mm x 60 x 25 mm)
- RS BOS502 (attention, 502 has area for display, should use 503).
Design
- Cutouts for display, pushbutton, sensor, hole for calibration
- Printed customisation by factory or with sticker
Display/voltmeter
- Murata 3½ Digit, LCD Display Digital Panel Voltmeter DMS-20lcd-1-5-c
- DMS Application note 3: Analog Common and Reference in-out
- DMS Application note 12: Signals with Zero Offsets
-
DMS Application note 2: Input Configurations, Power Supplies, and Ground Loops
- All models have an internal, 1- 2 microfarad, filter capacitor connected across pin 1 (+5V SUPPLY/+BATTERY) and pin 3 (5V RETURN/ –BATTERY) to attenuate high-frequency noise.
UV-sensor
- sglux SiC UV TOCONs / Broadband UV
sensor
- TOCON_ABC5
- Gives 0-5V output
- "Scatter" (tolerance) of ±20%. Should be able to calibrate this
out.
- See sglux FAQ: What about the TOCON scatter?
- Lower and higher sensitive sensors exist
Calculation of required sensitivity and sensor
- We want 0.2 MED/hr at 2V output = 0.5 MED/hr at full scale 5V output.
- Scaling factor is 0.24 MED/hr/W/m² so we want 0.5/0.24 = 2.08 W/m²
full scale
- Correction factor of 0.24 for a wideband TOCON ABC (that is more sensitive for UVA) to correct so that under natural sunlight gives same reading in med/hr as a perfect erythema meter.
- See Comparison of different UV sensors for use in an XP radiometer, A. Butterworth, December 16, 2018 (paragraph above Table 1).
- 2.08 W/m² = 2.08e-4 W/cm² = 208 µW/cm²
- The closest is ABC5 with 180 µW/cm² full scale.
- 0.2 MED/hr would then give an output of 0.2/0.24 * 1e-4/180e-6 * 5 = 2.3 V.
- The tolerance of the TOCONs is ±20%, some of them may not give us the required output: 2.3V*0.8= 1.84V instead of 2.000V. Should take this in account that 1.84V can be calibrated to read as 2.00V. 2.3V*1.2=2.76V. So calibration range must be 1.8V - 2.8V.
- For comparison 0.2 MED/hr should give 0.79 V on the TOCON E1. Calibration range 0.6V - 1V.
- Assuming the powers that are quoted by sglux are in W/cm² are normalised to the sensitivity spectrum of the sensor.
Likely not needed: digital calibration could be made with a TOCON Adjustment board (needs specific box to make setting).
Note that dependent on the design, the battery low indicator could not work (it turns on at 3.7V), or too late when the battery is almost empty. Vref would lower first, showing higher values than the actual one. This is a safe behaviour. Also, after roughly 6.5V a battery seems quickly to go to 0V. Until 6.7V we can have Vref still at 5.000V
Printed Circuit Board
- Holds
- TOCON
- Needs to be mounted at 90 degrees as on front-side of box.
- Needs an additional board?
- Ask sglux if TOCON can come with wires or a low-cost connector allowing assembly at 90 degrees
- Needs to be mounted at 90 degrees as on front-side of box.
- Push button (height should be right)
- Wires up to 9V holder
- Display/voltmeter
- Needs careful adjustment in height, or with socket that allows movement? Or wire the display up to the PCB?
- Allow for hole in PCB to reach calibration screw
- Resistors for the full-scale adaptation from 0-5V to 0-2V (1%
metal-film). Can be done with Vref.
- Tolerance of TOCON ±20%. Should be able to handle this. Can
be done with Vref. 1.8V should be able to read as 2.0V.
- Use high-precision potentiometer?
- Use selectable resistors?
- Use a digital potentiometer or sglux setting board/schematics (requires programming with special box and connector)
- Final fine (±50 counts or ±2.5%) calibration on Display/Voltmeter
- Tolerance of TOCON ±20%. Should be able to handle this. Can
be done with Vref. 1.8V should be able to read as 2.0V.
- TOCON
Various
- 9V battery
- Assembly: mask off the rightmost digit with tape or a dedicated sticker. Or possibly not even needed as no UV will read as 000 anyway.
Compliance testing
-
- Gives a good summary of the EMC standards
-
The meter needs to comply with general standards IEC 61000-6-3 and IEC 61000-6-2 which mandate for a battery-powered device:
- CISPR32 (Radiated emissions)
- IEC 61000-4-2 (ESD immunity)
- IEC 61000-4-2 (Electromagnetic field immunity 80 MHz – 2.7 GHz)
- IEC 61000-4-8 (Magnetic field immunity at 50/60 Hz)
Erik van der Bij - 10 October 2019 (28 November 2019 added "early ideas" section and page freeze)