Unknown Temperature Probe

[GerdW]

Hi swanholm,

I already pointed you on page 1 of the spec sheet saying you need a power supply of 4 to 30V.

How often do I need to repeat this?

Your 15V supply is perfectly fine!

[c-swanholm]

yeah man, I get that

The schematic on page 3 at the bottom shows a voltage source and the schematic also shows a 273mV battery in the bottom right corner as a reference voltage of some kind.

Not sure what the purpose of it is.

Regardless even if i just give the probe 15VDC and measure the current output I get nothing. Theres no change in current with changing temperature.

In fact if you measure the voltages like in the diagram i get 16VDC when using a 15VDC source.

I just don't understand the properties of this probe. The thing is making AC current out of DC current too. It acts like a diode but the resistance does change with temperature.

[RavensFan]

Why not just use a more normal temperature measurement device such as a thermocouple, RTD,or thermistor, where it is easy to find signal conditioning devices and circuits to read them?

[c-swanholm]

Believe me if I could I would've done that last week haha this thing is a pain.

I can't change the probe without reprogramming the computers my equipment interfaces with.

I'm trying to build a test station with labview equipment so i can just plug my machine in and run the program.

It sounded simple enough when I started. I've been able to control pumps, heaters, valves etc. but the feedback from the tool has been tricky. I think im missing a big piece of the puzzle. this is all supposed to interface with a computer that i dont have access to or any information to help me. It's called a general purpose temperature transducor... doesn't seem to be very typical to me.

I figured I was smart enough to read a simple temperature probe but maybe not!

Thanks for your help,

Christian

[GerdW]

Hi Christian,

the schematic also shows a 273mV battery in the bottom right corner as a reference voltage of some kind.

You don't need this additional battery, its just a reference! Just measure the output voltage.

After all the probe is a current source (or better: current limiting device) and you will measure the voltage drop over those resistors enforced by the current from your probe.

Each simple 4-20mA sensor will work using the very same principle: You supply a power source at one pin and the other pin is connected to GND. The sensor is limiting the current and you could use either a current meter or some shunts to measure voltage drop!

Regardless even if i just give the probe 15VDC and measure the current output I get nothing. Theres no change in current with changing temperature. In fact if you measure the voltages like in the diagram i get 16VDC when using a 15VDC source.

Is your probe still working properly? Did you check with a second (or third) probe?

-

[c-swanholm]

I beleive it's working correctly. I can measure the resistance of it no problem. I start having issues when it's connected to a power source. When put my meter inline with the circuit (switching my leeds) I get no current output from the probe. I believe it's inducing current. From what I understand an inductor in a dc circuit acts like an open once it builds charge. Like I said, it makes AC out of DC. I measure no output current. I measure a negative voltage across the probe and a voltage greater than my source across the other resistor. It also acts like a diode. Pretty weird stuff. People in my shop have no idea. I've had people check my work. I showed it to my supervisor who has a masters in electrical engineering and he said he didn't know haha.

Maybe there is an issue with the probe but I don't have one to compare it to at the moment. I've ordered an LCD display that integrates with these sensors so hopefully that works, it was cheaper than the probe. Supposedly has analog outputs that I can use to communicate with labview.