Is there anything which mimics a UV sensor? - Page 1
Forum section: electronics / repair

author: bypassrestrictions
author_rank: Contributor
timestamp: January 28, 2022, 07:04:08 am
content: I don't know if the UV sensor is a diode or an LDR but it is damaged and not working.It looks a lot like this:Inside I can see squiggly lines like LDR has but I'm not getting such images when I search for LDR, I only get such images if I search for photo diodes.So is there anything which mimics a UV sensor?

author: Ian.M
author_rank: Super Contributor
timestamp: January 28, 2022, 07:45:56 am
content: There are multiple sensor technologies that can be used for UV detection/measurement, so you'll need to determine the part number and find a datasheet to know how (or even if) you can fake it.

author: bypassrestrictions
author_rank: Contributor
timestamp: January 28, 2022, 09:01:33 am
content: Quote from: Ian.M on January 28, 2022, 07:45:56 amThere are no part numbers on the component.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 28, 2022, 10:59:42 am
content: Google GUVV-T10GD-L for a similar looking device.http://www.geni-uv.com/download/products/GUVV-T10GD-L.pdf

author: bypassrestrictions
author_rank: Contributor
timestamp: January 28, 2022, 01:28:31 pm
content: If it was a diode, wouldn't the device have worked if I just directly connected the positive and negative.Since the device didn't work, I'm guessing it could be a resistor.

author: Fraser
author_rank: Super Contributor
timestamp: January 28, 2022, 01:48:45 pm
content: You need to provide more detail of where the sensor is being used. What is the purpose of the equipment and the sensor within it ?As has been stated, there are many different types of device that may be used to detect UV wavelengths of light. I have worked with the gas cell UV types of detectors but filtered optical diodes and CCD’s are commonly used these days.If, in your last post you were asking whether replacing the suspected diode sensor with a bridging wire would work, the answer is no.If the device you are trying to repair has safety related controls applicable to it, I suggest you consider your personal or company liability situation.To do:Tell us what equipment this sensor resides withinTell us why it is needed in that equipmentTell us whether the equipment is in any way controlled in terms of safety regulationsShow us pictures of the PCB on which the sensor is mounted (both sides)Only then can anyone offer any meaningful comment beyond our best guesses.Fraser

author: bypassrestrictions
author_rank: Contributor
timestamp: January 29, 2022, 12:18:31 pm
content: Quote from: Fraser on January 28, 2022, 01:48:45 pmThe UV sensor is part of last stage of water purification, the UV is connected to two long thin wires are part of two other sensors, these 3 pairs of wires go into the PCB, I'm guessing the UV sensor is there to check if the light bulb being used in the UV disinfection stage of water purifier is indeed a UV light and not some normal light bulb.

author: Fraser
author_rank: Super Contributor
timestamp: January 29, 2022, 01:43:27 pm
content: A UV sensor can be used in this application to detect that the UV light is present and the UV source has not failed. It can also monitor ageing of the UV source to indicate when that source is at the end of its useful life. In the first instance the UV sensor can form part of a simple on/off detector that tells the controller whether the UV light source is operational, or not. In the second instance the UV Sensor is part of an analogue level monitor that would likely feed an ADC for the controller board to monitor ageing of the light source. That level signal also acts as a ‘UV on and present’ sensor. In some systems the analogue signal from the sensor is used to set the drive level on the UV Source in order to maintain the correct emission of UV for the sterilisation process. Anything that is a professional steriliser should provide assurance that it is doing its job properly and warn if the UV light no longer meets the needs of the sterilisation process.Can you post a picture of what may be seen through the sensors window ? I would have expected a small square of silicon with two bond wires attached to it. Some smart sensors have quite a complex looking IC die visible through the window. You mention the possibility of a LDR. I have not seen a UV responsive LDR but I suppose one could be made if the right UV sensitive materials were used.If you have three of these sensors, can you not test them to determine whether they are diodes, LDRs or some more complex component like an IC ? Surely all three cannot be faulty ?FraserFraser

author: Fraser
author_rank: Super Contributor
timestamp: January 29, 2022, 01:48:37 pm
content: Yep, UV photo responsive resistors (LDRs) exist and cover IR to UV…..https://www.senbasensor.com/products/ldr-photoresistors/Picture of D57 sensor attached. It appears to match your descriptionIf you are dealing with an LDR, these are usually very reliable and not prone to failure unless abused. I suppose the UV can age them thoughIf one has died and there are others in the system, you can remove a good one and try to profile its optical response n order to identify a suitable replacement. As I said previously though, when dealing with anything Health or Safety related, you need to consider you liability fir tampering with it in any way, especially substituting components that are not identical to the original parts from the OEM. An LDR should be pretty easy to test for functionality thoughFraser

author: Renate
author_rank: Super Contributor
timestamp: January 29, 2022, 02:47:13 pm
content: QuoteI find that an inhabitant of the UK turns bright pink under the presence of UV light.

author: bypassrestrictions
author_rank: Contributor
timestamp: January 29, 2022, 04:42:32 pm
content: Quote from: Fraser on January 29, 2022, 01:43:27 pmNo, I cannot post a picture because I have already put it together and taking it apart would be an onerous task. One is a weight sensor, one is UV sensor and I don't know what the other sensor is.

author: bypassrestrictions
author_rank: Contributor
timestamp: January 29, 2022, 04:54:04 pm
content: Quote from: Fraser on January 29, 2022, 01:48:37 pmYes, it clearly appears like someone sabotaged the sensor, there were scratch marks all over the hole holding the UV sensor harness, someone must have painted an obstructive paint, which doesn't allow UV light to enter the sensor, I can only guess the motive, but I'm sure it is nefarious and malicious. Because presently I'm not in a state to buy a new water purifier, so the only option left is to buy bottled water or trick the PCB into thinking the UV sensor is working, in case I trick the PCB, there is the risk of someone replacing the bulb with a dead one or normal bulb which wouldn't disinfect the water.

author: Fraser
author_rank: Super Contributor
timestamp: January 29, 2022, 04:55:13 pm
content: Well it looks like you have your answer…Likely technology : UV Photo sensitive Resistor (LDR)Dark Resistance : Not KnownMaximum exposure resistance : Not knownDesign resistance in the specific application that you have : Not knownSadly in order to replace this component you would need a good one for testing purposes.The circuit could be tested using a potentiometer in place of the LDR. You would adjust the potentiometer until it’s value was recognised as valid by the circuit to which it is connected. Start by choosing a potentiometer that covers the common ranges of LDR resistance and see how it goes. If the control circuit is used to set the UV source drive, make sure you chose a start resistance that equates to a very bright scene being viewed by the LDR. This avoids over driving the UV source.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: January 29, 2022, 05:14:55 pm
content: In case you are wondering, if I were testing the controller board, I would place a 10K potentiometer across the UV sensor input and initially set it to around 1K Ohm to simulate a very bright scene resistance. The UV source may not light at this value if it is a variable drive system. Increasing the resistance of the potentiometer (to simulate an LDR seeing a lower intensity scene) in a variable drive system should increase the drive level just like if the ‘LDR’ intensity value is below that preset on the controller.In a simple on/off detector design, the value of resistance just needs to be low enough to look like a well illuminated LDR so around 2K Ohm should work but do not be tempted to use a shorting link as that is not advisable.