Hi
Currently working on a PT1000 interface with a tranzorb SMAJ5.0 (5V), but they are certainly not equal from different manufactors
Main parameter for the application is leakage current at 5V applied voltage:
Luckily we are using the ST part, and it measures well. In the lab, at around 3nA at 25 degrees, with very limited additional current at 85 degrees
Cheers
Klaus
Low voltage zeners are very soft.
Do you have 5 volts across the RTD?
søndag den 12. september 2021 kl. 04.25.00 UTC+2 skrev snipped-for-privacy@highlandsniptechnology.com:
0.5V-1V sounds much more reasonable for a PT1000
Self-heating should always be thought about for temperature sensors. 5V would give you 25mW. 0.5-1V is 0.25 to 1 mW, which would be a bit high for an NTC thermistor - 1mW produced 0.2K of self-heating in a situation that I commented on in Rev.Sci.Instrum.
Sloman A. W. “Comment on ‘A versatile thermoelectric temperature controller with 10 mK reproducibility and 100 mK absolute accuracy’ [Rev. Sci. Instrum. 80, 126107 (2009)] “, Review of Scientific Instruments 82, 27101 - 027101-2 (2011).
Platinum resistance sensors have a positive temperature coefficient, so you aren't going to make them unstable by dissipating too much heat in the sensor, and their thermal resistance to ambient can be lower than you can get with a thermistor.
Sloman, A.W. "On microdegree thermostats", Journal of Physics E: Scientific Instruments, 11, 967-968 (1978).
On a sunny day (Sun, 12 Sep 2021 02:46:10 +0200) it happened Klaus Vestergaard Kragelund snipped-for-privacy@hotmail.com wrote in <shjikj$hdo$ snipped-for-privacy@gioia.aioe.org>:
Nice varicap...
Only 1V, so the we are way down on the curve
Yes, looks like somebody just drew a line on a graph ;-)
When I need low leakage, one trick is to bias the transzorb at a higher voltage than the input and connect them with a low leakage diode
It is not the valtage that is changed, it is the part with its breakdown voltage...
On a sunny day (12 Sep 2021 10:10:25 GMT) it happened Uwe Bonnes snipped-for-privacy@hertz.ikp.physik.tu-darmstadt.de> wrote in snipped-for-privacy@mid.individual.net>:
OK, I see, was already thinking about possible applicaions.
Too good to be true...
Or just clamp transients to +2 and -0.6 volts or something with plain diodes.
Or for ESD, just put a cap across the input. Temperatures don't change fast.
Power diodes can be huge-c varicaps, but the tempcos are horrible.
Ditto but worse for high-K ceramic caps.
This should be no surprise.
These parts are not originally designed for low leakage or signal line applications.
RL
It works with ESD, but very difficult to find a 50A surge rated capacitor
I was surprised that for same part number the leakage is a factor 40 between different suppliers
SMA is a colloquial mechanical standard, loosely compliant with DO214Ax (but don't count on it). 'J' indicates leads formed under the body, rather than outwards (gull wing)
Adoption into part naming is a sales attempt at grouping generic parts with similar mechanical shape.
RL
Quite often the leakage they claim is the leakage they are willing to test for.
It takes quite a while for the stray capacitance to charge up far enough that the "leakage current" gets down to 3nA.
Somebody with a faster production line might settle for a higher leakage specification that they could test to faster.
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