Hi,...and while at it would you please expand on what you mean by "20 samples per second". Very few thermal sensing technologies can settle to a step change to high accuracy in that short of a time period.
Finally larger thermocouples made with heavier gauge wire will have even slower response times. You have not defined temperatures or temperature change, other than K you have not defined your Type K thermocouple. As to a thermocouple amplifier there are dozens of turn key solutions out there and available. A simple Google of Thermocouple Amplifier will bring up a dozen results. You also need to consider the response times of anything connected to the Thermocouple. The amplifier isn't the problem, getting a thermocouple to respond to changing temperature as fast as you want is the problem and again, I see no mention of temperature range or anticipated slew rate?The “Time Constant” or “Response TIme” is defined as the time required to reach 63.2% of an instantaneous temperature change.
Hi Ron,I really suggest you give this a read Thermocouple Response Times and become familiar with thermocouples and their characteristics as well as uncertainties.
Finally larger thermocouples made with heavier gauge wire will have even slower response times. You have not defined temperatures or temperature change, other than K you have not defined your Type K thermocouple. As to a thermocouple amplifier there are dozens of turn key solutions out there and available. A simple Google of Thermocouple Amplifier will bring up a dozen results. You also need to consider the response times of anything connected to the Thermocouple. The amplifier isn't the problem, getting a thermocouple to respond to changing temperature as fast as you want is the problem and again, I see no mention of temperature range or anticipated slew rate?
Ron
Whatever blogs you were reading, don't read them any more. READ THE AD8495 DATA SHEET. If you do that, you'll see that the frequency response of the AD8495 is down 3 db at 25 kHz, which corresponds to a response time of about 15 μs. That's microseconds, not milliseconds. So the AD8495 is over a thousand times faster than you need it to be, and therefore should be well suited for the job.Right now i am using Ad8495 as thermocouple amplifier. I found on some blogs that its response time fast enough(20ms).
Of course it's OK to use it. Whether or not you can get 20 ms response time from your thermocouple is another matter entirely, and will largely depend on the size and thermal mass of the thermocouple, the thermal conductivity of the liquid it's immersed in, and whether the liquid is moving and if so, how fast.Means i want to see the temperature change within 20ms in my graph on labview Is it okk to use it.
Thinking further about this. I have used Inor Temperature Transmitters in the past but this sort of unit has a dozen manufacturers and even more distributors. Temperature Transmitters take the mV signal from your thermocouple and convert it into a usable signal. For example a Type K thermocouple signal can be converted to a specific range and scaled to a 4 - 20 mA output. That 4 to 20 mA is passed through a 500 Ohm resistor giving you 2 to 10 volts which you run into an A/D converter. Using a 250 Ohm resistor you could get 1 to 5 Volts. Either way the speed of the A/D conversion (Samples Per Second) is a function of the A/D converter. Then you can run that signal or look at it in any software solution you wish, I covered this in post #3.Hi All,
Thanks for the reply. I am using K type thermocouple and wants to measure liquid temperature with thermocouple.
I mean i want to see the change in temperature within 20ms. if temperature changes within 20ms then thermocouple amplifier should be able to amplify it with in that time period. i wants to see these results on y labview interface.
Thanks
Siddharth
You still need to run the amplified signal into a A to D and the sample rate of the A/D needs to meet your requirements. Normally liquid temperatures do not change very fast but your A/D sample rate is what will be plotting your curve.The AD8494/AD8495/AD8496/AD8497 are precision instrumentation amplifiers with thermocouple cold junction compensators on an integrated circuit. They produce a high level (5 mV/°C) output directly from a thermocouple signal by combining an ice point reference with a precalibrated amplifier. They can be used as standalone thermometers or as switched output setpoint controllers using either a fixed or remote setpoint control.
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