Infrared pyrometer - Page 1
Forum section: electronics / repair

author: Baigars
author_rank: Newbie
timestamp: October 05, 2025, 06:38:12 pm
content: Hello my centrifugal vacuum casting machine is not showing temperature of the crucible, the infrared pyrometer probe is not sending any data.Problem was that that the voltages ware switched. When the probe is disconnected, and sens pin is shorted to ground machine shows 1120c and when applied the 15v it shows 2000c, it is linear when i increase voltage the degree increases, checked the infrared pyrometer with oscilosccope it responds to heated metal and flame, so the opamp is damaged, but the markings are removed, so the question is is it possible to identify what kind of opamp it is?scheme the 4 pins are with o gnd +15 and -15bottom pcbinfrared pyrometer there is 1336 and bk3h markings not shure what this part is it, but it corresponds when i measure flame or heated metalthe unknown opamp damagedthe infrared pyrometer, topcast code A29084 for new one 4,2k eur. it is too much.Hope you understand why i don't want to buy this part, the capacitator sizes i did not measure.On the main board there is lot of ad, ti and st parts.any ideas what kind of opamp it is and what else i need to measure or add picture?Thanks

author: Baigars
author_rank: Newbie
timestamp: October 05, 2025, 06:47:22 pm
content: My probability is that it can be AD620,OP07 or INA128. But im not shure first i will listen to experts.

author: Swake
author_rank: Frequent Contributor
timestamp: October 05, 2025, 07:57:58 pm
content: That is not going to be an easy one.But there might be an alternative:- Handheld infrared thermometers that will measure up to 2000°C (3600°F). Cost about 50€ to 100€example:https://nl.aliexpress.com/item/1005007169532287.html(the blue one)1600°C models are a little cheaper.- There are 'industrial' sensors too, these output a standard 4-20mA signal. bit more expensive at 200€ to 400€example:https://nl.aliexpress.com/item/1005004508633484.htmlanother:https://nl.aliexpress.com/item/1005009810227161.htmlDisplay is about 10€https://nl.aliexpress.com/item/1005006288441199.html

author: wraper
author_rank: Unknown
timestamp: October 05, 2025, 08:40:25 pm
content: I'm 95% sure it's dual opamp with the most common pinout like LM358 and many others use. Certainly not a single opamp IC. You could measure with multimeter in diode mode between input pins 2-3 and 5-6 to figure out if there are protection diodes in between of those. Should narrow down possibilities. PCB looks like someone DIYed it with PCB etching using toner transfer.

author: Swake
author_rank: Frequent Contributor
timestamp: October 05, 2025, 08:53:17 pm
content: With the pins of the DIL-8 chip 'converted' to SMD.... that PCB is an oeuvre d'art!

author: wraper
author_rank: Unknown
timestamp: October 05, 2025, 08:55:23 pm
content: BTW this looks more like photodiode, and I don't know of any 2 pin PIR sensors. Here is the circuit in understandable way.

author: Baigars
author_rank: Newbie
timestamp: October 06, 2025, 11:08:50 am
content: Yes you are right it measures like diode and again yes thehttps://www.circuit-diagram.orgit is not very nice circuit drawing program, but it was first on google search.So ok dual opamp is more feasibleit mesures like thisone possibility is to get some nitric acid it needs to be some markings on the die, or just add lm358 and test on machine

author: wraper
author_rank: Unknown
timestamp: October 06, 2025, 11:57:03 am
content: LM358 should work, not sure how well though. Your measurements look like it could be a CMOS opamp, although there are not many of them that can work from 30V supply, the vast majority are low voltage ones. I would try TL072.

author: Baigars
author_rank: Newbie
timestamp: October 06, 2025, 10:16:19 pm
content: I did not have lm358 in dip pakage, but i find gl358, it coresponds now to flame,https://failiem.lv/u/mnv5j957nrSo you think the original part is like a TL072 or even an OPA2277, need to order that one.the strange part is that on switch position h the temperature barely increases, on l it is in video.thanks for Help.

author: wraper
author_rank: Unknown
timestamp: October 06, 2025, 11:53:44 pm
content: I don't think original is TL072 as it's JFET input but otherwise bipolar (except very recent revision from TI which they transitioned it to full CMOS) but your measurements look more like CMOS, however I think it should work just fine in this application. OPA2277 of course have better spec and should work fine too.

author: Swake
author_rank: Frequent Contributor
timestamp: October 07, 2025, 05:27:04 am
content: If it works with the gl358 why would you change it again?You risk damaging the PCB or other components.

author: wraper
author_rank: Unknown
timestamp: October 07, 2025, 07:39:44 pm
content: ^Its high input bias current adds to the transimpedance amplifier's error, therefore may affect the reading to a noticeable extent.