Your schematic does not show pin 4 connected to ground.thanks Ron! I wasn't sure if I needed one there.
Good catch. I didn't notice the ± in the first post.if your truly looking for a +/- 3000 range, you should retain the negative supply (with cap). This assumes that your DAQ allows provides for a +/- input.
If so, make sure your polarity on the cap is correct with respect to ground (+ terminal to ground).
I alluded to this question in post #12, and the OP didn't challenge measuring only a positive load. But maybe he didn't get the point of my less-than-direct question....if your truly looking for a +/- 3000 range...
noted,I alluded to this question in post #12, and the OP didn't challenge measuring only a positive load. But maybe he didn't get the point of my less-than-direct question.
I helped on a very similar project about a month ago. I suggested a null scheme in post #61. It's not perfect, but it might be good enough.noted,
nulling the output would require a negative bias, unless full scale reduction and compensation was employed with the ADC.
Eventually I need it to read both compressive and tensile forces so I will need the full +/- 3k range (though the mechanism will not ever exceed 1.5k lbs). I was thinking of amplifying it so that 10V = 1.5k lbs in order to get better resolution but I'm not sure if that makes sense.if your truly looking for a +/- 3000 range, you should retain the negative supply (with cap). This assumes that your DAQ allows provides for a +/- input.
If so, make sure your polarity on the cap is correct with respect to ground (+ terminal to ground).
I wish I understood what you meant here. I am just reading the voltage and have a software tare that accounts for the voltage at zero load then in subsequent measurements I just subtract that voltage before figuring out the actual load. Am I talking about the same issue here or am I completely off?I helped on a very similar project about a month ago. I suggested a null scheme in post #61. It's not perfect, but it might be good enough.
More accurate output nulling could be done by temporarily applying a voltage divider to the reference input. The exact value is not very important, but a low voltage will keep common mode rejection (or lack thereof) from being an issue. Adjust the null pot while monitoring the voltage between the ref input and the output, and set it to zero. Then switch the reference input back ground. See the attachment.
Um... I just switched it and the capacitor blew up in my face... Are you sure about this? I'm hoping it didn't damage any other part of my circuit.If so, make sure your polarity on the cap is correct with respect to ground (+ terminal to ground).
If you have a single power supply, you may need offset adjustment to get the output off the ground rail, if it happens to be stuck there with no strain on the load cell. However, since you are doing software tare adjustment, you could just add a little offset to the Ref input if it is needed. If your output is positive with no strain, then you need to do nothing. Keep in mind that offset wastes dynamic range.I wish I understood what you meant here. I am just reading the voltage and have a software tare that accounts for the voltage at zero load then in subsequent measurements I just subtract that voltage before figuring out the actual load. Am I talking about the same issue here or am I completely off?
Go back and read the post carefully. He was referring to the cap on the negative supply.Um... I just switched it and the capacitor blew up in my face... Are you sure about this? I'm hoping it didn't damage any other part of my circuit.
Could you also please specify which capacitor? Do all of them have to be reversed? Please refer to my last schematic. I'm scared of changing anything now as I'm not sure if I'll blow up another circuit.
So after spending the last 15 minutes reading about this.. I had it right. Positive to higher voltage, negative to ground. Everything specifically warns against putting the positive terminal into ground. I'm not sure why you told me to switch it? Hope it wasn't deliberate.
I guess I misunderstood. I thought he was referring to my new (sans neg supply) schematic. Good to know though thank you.Go back and read the post carefully. He was referring to the cap on the negative supply.
That requires either returning to a dual supply or establishing a virtual ground at the midpoint voltage of a single supply.Eventually I need it to read both compressive and tensile forces so I will need the full +/- 3k range
so, is that a sunburn or are you just happy to see me?Um... I just switched it and the capacitor blew up in my face... Are you sure about this? I'm hoping it didn't damage any other part of my circuit.
Could you also please specify which capacitor? Do all of them have to be reversed? Please refer to my last schematic. I'm scared of changing anything now as I'm not sure if I'll blow up another circuit.
So after spending the last 15 minutes reading about this.. I had it right. Positive to higher voltage, negative to ground. Everything specifically warns against putting the positive terminal into ground. I'm not sure why you told me to switch it? Hope it wasn't deliberate.
Yeah my output at no strain is ~0.01147 V. So by what you said, is this fine since its not in the negative range?Did you see post #31?
Ideally I would like to get the full 12 bit resolution. As far as the input requirements of my DAQ go, here they are (this is a copy paste from the specs): "4 HV Inputs have ±10 Volt or -10/+20 Volt Range." This is what I went off of by trying to tailor the gain so that the maximum voltage after being amplified would land on 10V. My calculation was 10/20.0918E-3 = 478. Though initially when I did this I didn't account for the voltage at zero load. I also assumed 10V instead of the actual 9.95V for excitation. Is that 0.01147V throwing off my readout and causing me to get the wrong values since the actual thing spans 0.01147 - 10.### V? Also what is my load resolution in lbs? I thought 3,000/2^12 but now seeing as how my DAQ spans a total of 20V I think I may have miscalculated that.What we probably need to ask, is two fold, the input requirements of your DAQ and if you want the full 12 bit resolution over that input.