PT 100 4 wire temperature sensor

[John Tzoutzakis]

Hi everyone,

my name is John and i am a student at the technical university of
Patras,
Greece. I could really use some help here, with this RTD "PT 100"
temperature
sensor.
I have developed a temperature data acquisition system using a card,
connected to my PC serial port. I have tested it by using a LM 35
(requires Vcc = 5V) temperature sensor and it works. The thing is that
i want to adjust a PT 100 temperature sensor.
I bought one but...

The PT 100 has 4 wires (2 white, 2 Red), i have tried using my
multimeter to
measure the output but it doesn'y work (PT 100 ouput 1mV/Celsium). If
i connect it to my card then i get 0 input. I was expecting to get an
output from the sensor at about 30 mV. What am i doing wrong here?
Does anyone has any idea or experience about PT 100 temperature
sensors?

Thanks in advance

 

[Mike Harrison]

On 14 Oct 2003 12:09:13 -0700, jtzoutzakis@hotmail.com (John Tzoutzakis) wrote:

Hi everyone,

my name is John and i am a student at the technical university of
Patras,
Greece. I could really use some help here, with this RTD "PT 100"
temperature
sensor.
I have developed a temperature data acquisition system using a card,
connected to my PC serial port. I have tested it by using a LM 35
(requires Vcc = 5V) temperature sensor and it works. The thing is that
i want to adjust a PT 100 temperature sensor.
I bought one but...

The PT 100 has 4 wires (2 white, 2 Red), i have tried using my
multimeter to
measure the output but it doesn'y work (PT 100 ouput 1mV/Celsium). If
i connect it to my card then i get 0 input. I was expecting to get an
output from the sensor at about 30 mV. What am i doing wrong here?
Does anyone has any idea or experience about PT 100 temperature
sensors?

Thanks in advance

PT100 is a resistance sensor not a voltage generator.
If you feed it with a constant current, you will get a voltage output proportional to resistance,
but this then needs to be offset, scaled and linearised to convert to temperature. If high accuracy
is not required, you may be able to omit the linearisation.

 

[John Tzoutzakis]

Mike Harrison <mike@whitewing.co.uk> wrote in message news:<o9voovgh8f690mo993joqj7adcktk14evc@4ax.com>...

On 14 Oct 2003 12:09:13 -0700, jtzoutzakis@hotmail.com (John Tzoutzakis) wrote:

Hi everyone,

my name is John and i am a student at the technical university of
Patras,
Greece. I could really use some help here, with this RTD "PT 100"
temperature
sensor.
I have developed a temperature data acquisition system using a card,
connected to my PC serial port. I have tested it by using a LM 35
(requires Vcc = 5V) temperature sensor and it works. The thing is that
i want to adjust a PT 100 temperature sensor.
I bought one but...

The PT 100 has 4 wires (2 white, 2 Red), i have tried using my
multimeter to
measure the output but it doesn'y work (PT 100 ouput 1mV/Celsium). If
i connect it to my card then i get 0 input. I was expecting to get an
output from the sensor at about 30 mV. What am i doing wrong here?
Does anyone has any idea or experience about PT 100 temperature
sensors?

Thanks in advance

PT100 is a resistance sensor not a voltage generator.
If you feed it with a constant current, you will get a voltage output proportional to resistance,
but this then needs to be offset, scaled and linearised to convert to temperature. If high accuracy
is not required, you may be able to omit the linearisation.

Thanks Mike for the reply
a while after i posted the message and reading ny notes again i
realized it ... and yes you are right. I also found that there are
commercial linearisers compatible with the PT 100 temperature sensor
so i got one and "yes" it works.
The only problem is that i get noise on my measurements... so i am
thinking of getting a battery for the lineariser's power supply.

Thanks again