I'm at work right now....

I am trying to measure the voltage through a "DaqPro", basically a data logger. I've used a voltmeter to get a reading, but then when I use the DaqPro it's totally off. So my question is--what does loop impedance mean, especially if it reads:

(Input Channel Measure: 0 – 50.000 mV)

Range 0 to 50mV
Resolution 3µV
Accuracy ±0.5% of reading
Loop impedance - 50O

Please let me know if you understand!

7/11/2006 9:01:22 AM

50 Ohms?

http://en.wikipedia.org/wiki/Impedance

7/11/2006 12:01:37 PM

can yall produce 1.21 jiggawatts?

[Edited on July 11, 2006 at 12:21 PM. Reason : .]

7/11/2006 12:04:45 PM

not really

7/11/2006 12:05:35 PM

Hi.

Let me introduce you to my roommate, Quinn.

7/11/2006 1:50:31 PM

hahahah DaqStations and Yokogawa as a whole can eat me


but for real,

check your ranges and spans in your DaqPro to make sure that they correlate to what you are expecting. if your span is off, you will get nonlinear relations to your source.

[Edited on July 11, 2006 at 3:04 PM. Reason : w]

7/11/2006 3:02:25 PM

?

7/12/2006 3:14:44 PM

... do you mean span as in what the sensor should be able to detect? I also don't know the difference between loop impedance and input impedance...

7/12/2006 4:15:43 PM

50 ohm impedence is fairly common for lab equipment, if not standard. I'm using a vector network analyzer among other lab equipment this summer, and all the ports are rated as 50 ohm ports. A lot of the couplers and adapters we have are 50 ohm rated, to ensure impedence matching.

7/12/2006 9:31:01 PM

hi

7/12/2006 10:39:48 PM

id help but im too busy blowing up 1/4 watt resistors with 8 watt loads due to short circuit zeners

7/12/2006 11:49:35 PM

^ i lol

7/13/2006 1:40:39 AM

a cute girl in ECE, tis not possible. TREASON

7/13/2006 2:24:33 AM

^who are we talking about?

7/13/2006 8:46:25 AM

forget it I'm just gonna tinker with the fluke meter and such. thanks though!

7/13/2006 10:43:08 AM

hey, does anyone have a time-domain reflectometer?

7/13/2006 11:13:20 AM

Are you just making up words or what?

7/13/2006 11:15:03 AM

haha, it's pretty much jibberesh to me, so I suppose so. Also, does anyone think that by calibrating something you can automatically assume that the impedances match?

Also, if the output of something is reading 200 mv and I want to step this signal down using resistors to below 50 mv (prob around 25), what size resistor should I use?

[Edited on July 13, 2006 at 12:08 PM. Reason : ]

7/13/2006 11:56:56 AM

its not impedences you calibrate.

you are attempting to calibrate your spans and ranges.

[Edited on July 13, 2006 at 12:12 PM. Reason : e]

what i am saying is that usually with DAQ* products you are using an external sensor, with a lead into the DAQ station.

say, a pressure meter, that transmits its data on a 4-20 mA scale. the range and span are sensor dependant, and need to be properly correlated to your measurement device.

say its a meter that reads 0-2000 psi, so therefore 4 mA would correalate to 0 psi, and 20mA to 2000 psi. so your measurment station needs to know your sensor properties, or it's range. the span would be the fact that it transmits between 4 - 20 mA. if your measurement system is improperly setup and then calibrated, youll get non-linear relations to your sensor. since this is a mV issue, the concept still holds, just is with voltage not current.

so it looks like you are just trying to read voltage definition straight from a lead, which is difficult b/ci fyou put your measurement device inline of your circuit, your iinput impedence will interfere with the rest of your circuit. you could create a side circuit for your measurement leads, whcih i assume is what you have done. just make sure that you dont push too much voltage into your measurement leads.

you can handle this by adding a resistor across the two terminals which your measurement leads are spread across. this will decrease your voltage into the acceptable range for your measurement station, but youll need to keep this in mind when you are taking your readings, or in most DAQ* products, you could change your settings to display the calibrated readings.

make sense?

[Edited on July 13, 2006 at 12:23 PM. Reason : e]

[Edited on July 13, 2006 at 12:25 PM. Reason : whoops, mA ]

[Edited on July 13, 2006 at 12:26 PM. Reason : god its been like 2 years since ive messed with DAQ, getting it all worng]

7/13/2006 12:12:02 PM

Yep! Got it (I think). I'll figure out for sure in two days. Thank you for your help!

7/13/2006 3:40:06 PM

np. hope it works.

Daq can be tricky

7/14/2006 8:33:28 AM

Im not sure about this one but I think that the Loop resistance may refer to what resistance is seen by the circuit from the multimeter. Essentially you should always want high resistance because it would act as an open circuit and allow the voltage/current to flow as it would. I am not familar w/ the Daq meters so I could be sounding like a complete idiot, but maybe i could be right... either way I will dedicate my genious/ignorance to QUINN

7/14/2006 11:31:29 PM

^yea I mean loop impedance, is just the impedance of the circuit you are completing i'm pretty sure, input impedance is the impedance inherent to the test equipment, but I don't think this was her problem, and it seems like she has it figured out now anyway

7/15/2006 9:40:31 PM