RTD - Maximum current without sensor damage?

pt1000 max current

What is the maximum current through RTD Pt1000, which should not cause sensor damage?

maximum current rtd

You can probably feed more than 100mA but what about internal heat internally generated by this current? Reading will have error caused by reason.
DrWho

pt1000 self-heating

I know that current more than 1mA can cause self-heating... and is not recommended....

But I have a sample RTD Pt1000, which stopped working in my demo/proto kit... I don't know why...
I suppose that the reason is bigger current, but can't understand how it can happen. If my current generator break - max current should be less than 5 mA....

Do you believe that these 5mA can break the sensor - Pt1000?

constant current pt1000

5mA*5mA*1000Ohm = 25mW, it WILL destroy the sensor for less then a minute. Use <1mA with controlled current generator and apply the current only when you are meassuring.

131 ohm equal to deg rtd

Yes, I read that recommended current for Pt100 is 1 mA (to prevent from self-heating) and for PT1000 0.1-0.2mA (max 0.5 mA to prevent from self-heating). I knew that the recommended current for Pt100 is 1mA, and supposed that is the same for Pt1000, nevertheless that the power dissipation is 10x compared to Pt100.

Thank You for your recommendation!

What should I do if I want to measure 24h non stop?
To start the current before measurement and to stop after measurement once per 5 seconds for example?

rtd 50 measure microchip

I suppose You have a low-pass filter in sensor signal path. If this filter has time constant 50ms You should apply the reference current ( 1 mA or less ) app. 500ms before measuring and stop it immediately after the conversion complete. This mode of opperation alows use of greater current and delivered more precise result, without selfheating.
Temperature changes are very slow process. In addition the sensor itself has very slow responce - more than 20sec. I think You should measure it about 2 times in a minute.

pt1000 rtd error

Thank you!

Yes, I'm planning to use schematic on fig.5 / page 4 in AN687 of microchip.

2 OpAmps are used for current generator, which requires Voltage Reference of 2,5V,
for example LM336Z2.5 or other.
1 OpAmp is used to make cable resistance compensation, when using 3 wire sensors
1 OpAmp is used as voltage preamplifier with 2 pole low-pass filter.

I'll upgrade the circuit to add support for stopping the current. For example with
simple stopping the Voltage Reference.

I should start the current generator minimum 1 second before sampling and should
stop it after measurement. I'll calculate the time to be sure that all transitional
processes should pass and when everithing becomes stable I should start sampling.

Starting and stopping current generator is a good idea.
But my problem is that I burned one RTD Pt1000 (bought from China, unknown
manufacturer) last week with 2.5mA current.
So this is my fears, not to burn more RTDs ))

My hesitation is what is the best set of constant current for Pt1000, gain of the
amplifier to be safe for the sensor?
Even in extreme conditions - defective OpAmps and etc (ocoz I'm not paranoic to
plan to protect the sensor in high radiation or lightning or etc...)?

Is it safe to use 1mA current with Pt1000, if the sensor is applied with the current
for 2-3 seconds per / each minute?

pt1000 compared pt100

Yes, it's safe but you will get wrong result. I'm afraid that the selfheating will rise the sensor temperature. If You wish You may check it by using different currents or periods. For example : 1mA for 100ms, 250 ms, 500ms and 1 sec.

pt1000 rtd schematic

Thank You for suggestions!

Ok, I will test Pt1000 with 1mA current and time on power 0.1 sec, 0.25 sec, 0.5 sec and 1 sec as You have described.
I will test this after some days because I havn't working RTD now.

I think that better solutions are to use 0.1mA, 0.2mA or 0.25mA current and Amplifier with G = 10, G = 5 or G = 4.

Here is my simple calculations:
Pt1000 with 0.2mA and Amplifier G = 5, short cable (Rwires = 0 ohm)
Urtd = 1000 ohm * 0.2mA = 0.2V (0 degree Celsius)
Uout = G * Urtd = 5 * 0.2V = 1V (0 degree Celsius)
Urtd100degree = 1385 ohm * 0.2mA = 0.277V
Uout100degree = G * Urtd100degree = 5 * 0.277 = 1.385V

If I use 12 bit ADC with reference 1.5V maximum temperature, which I can measure is approx 130 degree celsius and with precision 10 steps per degree celsius. (1 step equal to 1.5V / 4096 = 0.366mV and 1 degree celsius is from 3.9mV (0 degree) to 3.7mV (130 degree) due to non-linearity)

When I measure -200 degree celsius the Uout-200degree = 0.1849V.

My range is from -10 degree to 110 degree, so I'll have information loss, nevertheless I believe that it will be good for me.