[time-nuts] HP10811 current versus temperature

Neville Michie namichie at gmail.com
Thu Nov 22 23:41:00 UTC 2007


Hi,
the current temperature relationship should be nearly linear,
so if 100mA is needed at 20 C ambient and it follows that at 80 C
no heating is required, then the heating current will decrease at
about 1.7mA/K.
cheers, Neville Michie




On 23/11/2007, at 9:33 AM, Didier Juges wrote:

> Bruce,
>
> I have some 4 terminal current sense resistors at work, but they  
> are very
> low values (0.1 ohm and lower), so what I may gain at the sensor I  
> may loose
> in the amplifier. Right now, the 1 ohm resistor and OP-27 give a  
> voltage
> that is way out of the noise, as the curve shows. If I can find more
> temperature stable resistors for the instrument amplifier, then I  
> could use
> one of those 4 terminal resistors. I will see what I can get to  
> improve this
> setup. As it is, it may not be extremely accurate in absolute  
> terms, but it
> is precise and probably sufficiently relatively accurate for what I  
> want to
> do.
>
> What do you think of the 2mA/degree current sensitivity? Is it in the
> ballpark? I need to run the test much longer, and over greater  
> temperature
> variations, but I am still tinkering with it... The engineer's  
> curse :-)
>
> Didier
>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
>> Sent: Thursday, November 22, 2007 3:28 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] HP10811 current versus temperature
>>
>> Ideally you should use a 4 terminal current sensing resistor
>> and a high input impedance instrumentation amplifier.
>> A Thomas style 4 terminal resistor in a temperature
>> controlled oil bath would be nice, but failing that a low
>> tempco 4 terminal resistor will suffice.
>>
>> Bruce
>
>
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