Hello All, I have given a target hardware(Main board) which has PT1000 temperature sensor. To testing this sensor I have to design a testing hardware. This testing hardware tells for the particular temperature sensor channel, I want this particular resistance. to carry out this I have to use the digital resistor and configure it for the desired resistances. Can you please help me which Digital IC I can make use of to get the desired variable resistance?

 

Hi Anna.
Welcome to AAC.
Your question is difficult to understand, are you asking for an amplifier circuit design for the PT1000.? so that you can measure temperatures?

E

 

... or are you asking us to recommend a particular digital potentiometer?

 

Asking to recommend the particular digital potentiometer

 

Hi Anna.
Welcome to AAC.
Your question is difficult to understand, are you asking for an amplifier circuit design for the PT1000.? so that you can measure temperatures?

E

Yes, I wanted an amplifier circuit design for PT1000 which can give a variable resistance.

 

ok...what range of resistances do you need for the expected range of voltages out of the PT100 and what range of voltages do you expect?

Part 2: resistance to ground or resistance to something else (what else)?

 

ok...what range of resistances do you need for the expected range of voltages out of the PT100 and what range of voltages do you expect?

The range of the temperature is -80 degrees to +80 degrees based on the particular temperature it should give me variable resistance. to get the variable resistance I need to make use of digital resistors.

 

Thank you.

I will ask one more time:

Over the -80° to +80° temperature range what range of resistances do you need. While we are at it, how much resolution and accuracy do you need?

Is this resistance to ground?

 

The range of the temperature is -80 degrees to +80 degrees based on

based on what PT you have.
I found parts that give clear numbers. +80C=1328 ohms, 0C=1000 ohms, -55C=783 ohms. I cannot find good numbers on -80C.
How many different places do you want to test. It is very easy to make a digital switch that places 3 or 4 resistors across your connector. If you want to measure 100 different places you will need the digital pot. I think 3 resistors will make a good test.
-----------edited------------
Many digital pots have poor accuracy resistors.
Look at a CD4051 IC. It can switch 8 different values.

 

A PT1000 is a PTAT sensor (proportional to absolute temperature), so -80°C should be 707Ω.
There are two major problems that you have to overcome when using PT100 or PT1000 sensors - self heating, and cable resistance. That requires a low test current, which, in turn, gives a low output voltage.
How long are the leads to the sensor?

 

TS is asking for recommendations for a digitally controlled resistance to emulate a thermistor - that's quite clear to me from the their post... which for PT-1000 is 723 -> 2839 ohms (-70 ->+500degC), 1000ohms at 0degC.

The issue is that most digital resistors/pots are typically in the 10k region, and don't have the resolution to emulate the PT-1000 over any meaningful range. An analog muliplexer or switch with a bank of resistors is an alternative but setting suitable resistors across the range can be tricky,

@I am Anna : As this is homework help I cannot give you the complete answer, but what you require is a MOSFET operating in its ohmic region as a controlled resistance/current sink - here is an example... the voltage Vtemp sets the current in Rsense which generates the same voltage at Vptc as the sensor would generate. The opamp U1 adjusts rhe gate voltage of the MOSFET to conrol the current flowing through it and hence both the sense voltage Vsense and the sensor voltage Vptc.

You need to figure the values of Vref, Rsense to give an appropriate range of Vptc and then identify the values of Vtemp to give the required current in Rsense. Vtemp would typically come from a digital to analog (DAC) converter driven by a MCU, and you'd monitor Vptc via an ADC to validate the resistance setting.

 

Hi,
The TS stated The range of the temperature is -80 degrees to +80 degrees , not +500C

The TS also stated: , I have given a target hardware(Main board) which has PT1000 temperature sensor. To testing this sensor I have to design a testing hardware.

The TS also stated: Yes, I wanted an amplifier circuit design for PT1000 which can give a variable resistance.

Also: to get the variable resistance I need to make use of digital resistors.

It finally became clearer what the TS wanted, due to the questions we asked in our posts

E

 

Hi Anna,
Please ask your tutor to confirm/clarify what he means by 'digital resistors'.
This type of resistor normally requires some external electronic method of selecting the digital resistance values.
Also, the selected resistance steps of a digital resistor are discrete fixed values, with a limitation on the number of resistance steps which can be selected.

E

 

Hello,

For -80 the resistance is 683,25 Ohm
For +80 the resistance is 1308,97 Ohm.
See the attached reference.

Bertus

 

Hi,
For reference only, LTS simulation of PT1000, using @bertus 683.25R > -80C, 1308.97R > +80C


E

 

The range of the temperature is -80 degrees to +80 degrees based on the particular temperature it should give me variable resistance. to get the variable resistance I need to make use of digital resistors.

Are those temperatures in Celsius or Fahrenheit?

 

Are those temperatures in Celsius or Fahrenheit?

The values I have given are for degrees celcius

 

The values I have given are for degrees celcius

As most of the other respondent's are. But the question is what temperature scale the TS is wanting. The range is a bit odd on either scale, so it's not a slam dunk for my crystal ball. Plus, the TS needs to learn to pay attention to these kinds of details.