Analog Fluctuation, Bad card?

[danw]

Your attached DVM photo (post #1) shows a value of 7.2V. But that's more than an expected 6.0 volts from a the 1:2 voltage divider across a 12.0V battery.

But if the battery was in a charging circuit, 7.2V is about where a lead acid 12V battery charges: 14.4V.

If you have a charger involved, the DC side is probably at different ground potential, causing common mode problems for a single ended AI (a typical symptom of that kind of problem is that the other channels are affected).

The test of a charger-related problem on a single-ended AI would be to disconnect the charger and see how a floating battery works on the voltage divider/AI.

 

[Davis_1377]

Your attached DVM photo (post #1) shows a value of 7.2V. But that's more than an expected 6.0 volts from a the 1:2 voltage divider across a 12.0V battery.

But if the battery was in a charging circuit, 7.2V is about where a lead acid 12V battery charges: 14.4V.

If you have a charger involved, the DC side is probably at different ground potential, causing common mode problems for a single ended AI (a typical symptom of that kind of problem is that the other channels are affected).

The test of a charger-related problem on a single-ended AI would be to disconnect the charger and see how a floating battery works on the voltage divider/AI.

That was doing a test with a seperate battery and a buck converter to test the voltage range. Ive also tried it with a 9v battery and potentiometer without the divider to get 7.17v to the card with the same fluctuation. grounding things different ways and resistance here and there dont affect it

 

[danw]

If you put a floating, 9V battery across a 0-10V AI card's (+) and (-) and only get 7V, you have a bad AI card.

 

[drbitboy]

new info. for some odd reason when the input voltage is at the certain point and the fluctuation starts it is making the other 3 channels jump around between 0 and 32769. the other 3 channels are shorted together. When I do get a good reading the other 3 channels set on 0.

more grasping at straws:



So I assume this is a 12-bit (single-ended) A/D (2940/4096 = 7.17/10), and 32769 (8001h) is a bit of a unique value, well outside 12 bits; is it possibly an error code from the card telling you that summat is out of whack?


Also, how many bits are in that fluctuation?

 

[Davis_1377]

If you put a floating, 9V battery across a 0-10V AI card's (+) and (-) and only get 7V, you have a bad AI card.

If I hook the 9v directly to the card it reads 8.5v and thats correct but as soon as I do the other 4 channels start jumping around.

 

[Davis_1377]

more grasping at straws:



So I assume this is a 12-bit (single-ended) A/D (2940/4096 = 7.17/10), and 32769 (8001h) is a bit of a unique value, well outside 12 bits; is it possibly an error code from the card telling you that summat is out of whack?


Also, how many bits are in that fluctuation?

I used the program it shows in the manual so it puts each CH into its own v memory location itself.

as far as how many bits i am unsure exactly how many but when i connect the 9v it makes the other channel increase by about 86 and jumping around. I know when the input is changed on any channel it makes the others move around with it no matter what i do. This feels like something internal or programming to me.

 

[rootboy]

If you tried it off of a 9 volt battery and it's giving the same results then I would suspect the card, since the battery shouldn't be fluctuating at all. Do you have a scope? And where in Tennessee are you located?

 

[Davis_1377]

If you tried it off of a 9 volt battery and it's giving the same results then I would suspect the card, since the battery shouldn't be fluctuating at all. Do you have a scope? And where in Tennessee are you located?

Vonore, Tn. I don’t have a scope. Thought about buying one just for this. The 9v affects the other channels too but not always

 

[rootboy]

Vonore, Tn. I don’t have a scope. Thought about buying one just for this. The 9v affects the other channels too but not always

Way over yonder then.

I have a 1054Z which has been upgraded to a 1104Z. I can't recommend it enough.

 

[Davis_1377]

Way over yonder then.

I have a 1054Z which has been upgraded to a 1104Z. I can't recommend it enough.

Cool thanks ill look into it. Ive noticed when i unhook all power from my analog card and wait, hook it back all readings are high and gradually lower. I guess warmup is to blame for that.

 

[drbitboy]

Vonore, Tn. I don’t have a scope. Thought about buying one just for this. The 9v affects the other channels too but not always

"There's an app for that" i.e. to use the microphone jack on a smartphone or tablet as a 'scope probe.


There would be some more signal conditioning involved of course, but it goes into the kHz range (audible sound).

 

[rootboy]

Cool thanks ill look into it. Ive noticed when i unhook all power from my analog card and wait, hook it back all readings are high and gradually lower. I guess warmup is to blame for that.

Odd. Maybe cap discharge? Out of curiosity, what is this on?

 

[Davis_1377]

Odd. Maybe cap discharge? Out of curiosity, what is this on?

Not sure if so mabe internal. Lol! Its a home automation system I built. Monitors water flow and speed for usage and leak detection. Driveway alerts also sends texts to our phones. Powered by 2 big deep cycle batteries with automatic RV charger/power supply, 3000w inverter to power my house during outages. PLC controls inverter thru the remote port and transfer relay in breaker box. Smoke alarm text and water heater temp.

 

[rootboy]

Very cool!


Your analog input card either requires a separate power source, or it can use the rack provided power, but using the rack power really isn't recommended. (this was mentioned by Mill_Control).

Another person mentioned that you could power your card from 12VDC, but the PDF states that it needs 18 - 26.4 VDC to operate. So could we see a picture of how you have it wired up please?


The part of the PDF that addresses the internal power supply and the hit you may take on accuracy:

"The DL205 base has a switching type power supply. As a result of switching noise, +/- 3–5 counts of instability may be noticed in the analog input data if this power supply is used. If this is unacceptable, try using one of the following.
1. Use a separate linear power supply.
2. Connect the 24VDC common to the frame ground, which is the screw terminal marked on the screw terminal marked “G” on the base.

By using these methods, the input stability is rated at +/- 1 count."


So how are you powering the input card? And how do you have the channel selection jumpers connected as well as your input selection jumpers? (either J2 or J3 depending on the date code of the module).

 

[Davis_1377]

Very cool!


Your analog input card either requires a separate power source, or it can use the rack provided power, but using the rack power really isn't recommended. (this was mentioned by Mill_Control).

Another person mentioned that you could power your card from 12VDC, but the PDF states that it needs 18 - 26.4 VDC to operate. So could we see a picture of how you have it wired up please?


The part of the PDF that addresses the internal power supply and the hit you may take on accuracy:

"The DL205 base has a switching type power supply. As a result of switching noise, +/- 3–5 counts of instability may be noticed in the analog input data if this power supply is used. If this is unacceptable, try using one of the following.
1. Use a separate linear power supply.
2. Connect the 24VDC common to the frame ground, which is the screw terminal marked on the screw terminal marked “G” on the base.

By using these methods, the input stability is rated at +/- 1 count."


So how are you powering the input card? And how do you have the channel selection jumpers connected as well as your input selection jumpers? (either J2 or J3 depending on the date code of the module).

Please excuse my sloppy diagram i drew it up in 5 mins. Please note I have tried a seperate 24v battery and power supply for the analog, I have also grounded CH1 - to 24V - and to 12v chassis any where i could ground to no affect. I have tried a different base power supply that was 120v no affect. totally unhooked inverter, charger, transfer relays and sensors, no affect. isolated the whole system from earth ground with batteries and 9v to analog no affect.

I had the jumper configured for ch1 only until i had this problem i set it for 4 ch operation to try the other channels. and the jumper for 10v