LM35 temp sensor to give chart recorder output

[Jules]

I have a circular chart recorder which has a 0 - 1 voltage input for FSD on the chart. I want to display temps, and use an LM35 temp sensor so that minus 5 deg C corresponds to 0V, and 35 deg C corresponds to 1V. This is my annual range near London.
I have stabilized +5 and 0V available, and can add a ICL7660 to generate -5V, to read below zero.
Any circuit ideas please?
Thanks

 

[FRIED]

What is the impedance of the recorder, ie how much current at 1V?
Is the input isolated? Can probably be done with an LM10

 

[Russlk]

This circuit will do the job:
Hmm, part of the picture was clipped. R1 and R2 can be replaced with 100K if accuracy is not important.

 

[FRIED]

I make the gain 1/400mV = 2.5 so R4 = 15K, and Voffset = 83mV
Adjusting R2 will have little effect.

 

[Russlk]

You are right, Fried, the gain is too high. I will have to check my design program.

The LM35 outputs 50 microamps, so R2 adjustment should have an effect.

 

[FRIED]

It's capable of putting out 1mA with little change in output voltage, ignoring selfheating. Here is an LM10 circiut. It does not require closely regulated supplies.

 

[eblc1388]

I have a circular chart recorder which has a 0 - 1 voltage input for FSD on the chart. I want to display temps, and use an LM35 temp sensor so that minus 5 deg C corresponds to 0V, and 35 deg C corresponds to 1V

Rather than going to great length for negative supply voltage, you might consider the LM335 which does the same thing but has output in Kelvin scale at 10mV/K. So -5 degree C gives +2.6816V and 35 degree C gives+3.0816V.

It is a simple matter to offset it and give 0-1V output.

 

[Jules]

LM 35 sensor

Thanks gents for all the ideas. It looks as if the LM335 is a better bet in this circuit. I'm not sure about how to offset it though - any ideas would be useful. What sort of accuracy could I expect over the -5 to 35C range?
I've also had a look at the LM34 deg F version of the LM35. This outputs 0V at 0F, and 1 Volt at 100F (10mV / deg F) which is more accurate than the deg C version. It also reads below freezing, so no offset required. I'm planning to use up to 10 metres of lead to connect to the sensor - is this going to cause too much noise? Does anyone know of a cheap source of a LM34 - they don't seem to be widely available in the UK
Thanks.

 

[FRIED]

Can you get the LM10? Any of the sensors mentioned so far will give similar results. What current does the chart recorder require, ie 1V, what resistance? What sensor can you get?