Hi, I have just bought the PCS10 and amazed that there is no info with it, I want to record
4 temperatures with it using thermistors (identical). This must have been done before, can I just put a thermistor in series with a resistor, across, say a ten volt supply, as I would on the input to an op amp and measure the fluctuating voltage at the mid point ? Or do I need to go the whole hog and set up four op amps ?
Anyone any ideas ? suitable circuits ? experiences ?
Thanks…
[quote=“BunkyOhare”]Hi, I have just bought the PCS10 and amazed that there is no info with it, I want to record
4 temperatures with it using thermistors (identical). This must have been done before, can I just put a thermistor in series with a resistor, across, say a ten volt supply, as I would on the input to an op amp and measure the fluctuating voltage at the mid point ? Or do I need to go the whole hog and set up four op amps ?
Anyone any ideas ? suitable circuits ? experiences ?
Thanks…[/quote]
The PCS-10 has a sufficiently high input resistance (1MΩ) that no buffering would be needed with most common thermistors, so just use the thermistor as one part of a simple voltage divider and feed the PCS-10 from the junction of the two resistors.
Something like this:
I have assumed you wish to use an NTC thermistor, the modeled component (R1) is rated 5kΩ @ 25°C. Resistor R2 should be selected to be close to the mid-range resistance of the selected thermistor.
The output trace was created by manually varying the thermistor value from minimum to maximum (-20°C to 80°C)–the output voltage range of this divider (with the 10.0V supply) was 0.794mV to 8.83V.
The PCS-10 input is shown for reference only.
Thank you so much for that, I was hoping it would be that simple. I will change the value accordingly to match the thermistor, in fact put a pot in there so I can match each thermistor as accurate as possible to 25C, its the fluctuations I am interested in logging.
Many, many thanks again. Bunky.
[quote=“BunkyOhare”]Thank you so much for that, I was hoping it would be that simple. I will change the value accordingly to match the thermistor, in fact put a pot in there so I can match each thermistor as accurate as possible to 25C, its the fluctuations I am interested in logging.
Many, many thanks again. Bunky.[/quote]
It sounds as though you wish to compare multiple thermistors at a fixed temperature? If so then manipulate R2, and the supply voltage, to place the 25°C output in the “upper-end” of the selected PCS-10 input range. This will provide the most accurate measurement.
In the schematic below I have used a 6.0V supply, and changed R2 to 100kΩ:
This makes the output at 25°C 5.7V, a good match for the PCS-10’s 6.0V range.
However even doing this remember that the PCS-10 is an 8-bit device. The very best resolution you will get is 1/256th of the input range. With the 6.0V range this is a best case resolution of 0.0234V, real world resolution may be 0.05V or higher. This may not be adequate for the comparisons you wish to make.
