Hi.
Got a LM324 OP-AMP and when I supply it with +24V at VCC+ and GND at VCC- I get nearly 24V at almost all the other pins. Is that normal? Is it blown ?
+24V across the supply rails is safe for an LM324. Now, if you accidentally reversed the polarity so that there's actually -24V across the supply rails - it's fried.
Can you post a schematic AND an actual picture of your circuit?
Power_Broker:
+24V across the supply rails is safe for an LM324. Now, if you accidentally reversed the polarity so that there's actually -24V across the supply rails - it's fried.Can you post a schematic AND an actual picture of your circuit?
I think the schematic is correct. But I may have done something wrong in my circuit. What do you mean by supply rails?I tried to only connect 24+ and GND I get 24V on all the other pins to. Is that normal?
Thanks for helping !
can be normal...
U have to build i complete circuit and check that the output varies the way you expect.
Find (search "voltage follower") build , test..
knut_ny:
can be normal...U have to build i complete circuit and check that the output varies the way you expect.
Find (search "voltage follower") build , test..
Im a little afraid to connect the output (3OUT) to the span zero circuit. Becouse its 24v... And also I have a seperate voltage source at 5v that I would like to connect to 1IN+, but I'm also afraid to connect that becouse its already 24v on that pin.
That circuit isn't a schematic, its just a wiring diagram so its really hard to follow...
Anyway it appears to be some low pass filtering using far too many opamps and
includes a stage that looks like a Sallen/Key filter with an extra buffer stage spuriously
added in the middle - lord knows what response that will have.
The VR labelled R5 needs a capacitor across it to reduce noise given the high impedance,
and the not one opamp has any decoupling capacitors... Not likely to be stable if thats the case.
The offset and gain adjustments mean the output of the upper signal path could be rather
different from the input voltage.
The input sections suggest its to handle a pairs of 4--20mA current loop sensors.
Where did this circuit originate?
Seems like all of your opamp configs except for one are simply voltage buffers. This means that on all but one of your opamp outputs the output voltage should be exactly the same as the input voltage. The one odd opamp I haven't looked closely enough to figure it out. A proper schematic would help...
pederw:
I think the schematic is correct. But I may have done something wrong in my circuit. What do you mean by supply rails?I tried to only connect 24+ and GND I get 24V on all the other pins to. Is that normal?Thanks for helping !
The diagram you provided isn't a 'beginners' one.
If you're a beginner, as you mentioned, then start with a single LM324, and do some basic tests and exercises, such as to construct a non-inverting op-amp with a gain of approximately 2.
Also, note that single supply is being used here. So the input to the operational amplifier circuit with need to be appropriately biased (DC-biased).
Also - in your diagram --- the 4th op-amp component isn't being used. So look up information (online) that tells you what to do with unused op-amps ----- to ensure that its inputs aren't floating, and may become sources of noise due to floating inputs.
Southpark:
Also, note that single supply is being used here. So the input to the operational amplifier circuit with need to be appropriately biased (DC-biased).
They are DC biased if connected to current loop inputs, 250 ohm load resistors means the signals between
+1 and +5V at the inputs. The opamps in question are happy with signals down to the 0V rail anyway, its clear
from the filter time-constants and input circuit and 24V supply this is not an AC amplifier!
MarkT:
this is not an AC amplifier!
When I see labels saying 'filterinn' ....... then my assumption is AC. It might be the wrong assumption...... but AC is what I assume to begin with. Not necessarily an 'AC amplifier'. But a filter, involving AC.
Thank you all for taking your time!
Actually the only thing i need to know is if someone have a spare LM324. Add 24+V att VCC and GND att VCC-, then measure over the other pins, do you get 24+V or not?
MarkT:
That circuit isn't a schematic, its just a wiring diagram so its really hard to follow...Anyway it appears to be some low pass filtering using far too many opamps and
includes a stage that looks like a Sallen/Key filter with an extra buffer stage spuriously
added in the middle - lord knows what response that will have.The VR labelled R5 needs a capacitor across it to reduce noise given the high impedance,
and the not one opamp has any decoupling capacitors... Not likely to be stable if thats the case.The offset and gain adjustments mean the output of the upper signal path could be rather
different from the input voltage.The input sections suggest its to handle a pairs of 4--20mA current loop sensors.
Where did this circuit originate?
Okey. First of all, yes this is a filter for a 4-20mA loop. The op amp at the top is a filter(the one to the left) and the other one is e zero/gain circuit. The third opamp is also a filter for another 4-20mA loop with no zero/gain. I know the circuit work, becouse I have testet it in Multisim and also on the breadboard. But after I soldered it on a PCB the OpAmp for the Zero/gain got blown. I think that was becouse I solder something wrong. Now I have taken it apart and got the Zero/gain to work. But when I tried to make the first filter (topleft) I dont know if its normal to have to problem i stated before with the 24+ on all pins. This is for a school project.
Power_Broker:
Seems like all of your opamp configs except for one are simply voltage buffers. This means that on all but one of your opamp outputs the output voltage should be exactly the same as the input voltage. The one odd opamp I haven't looked closely enough to figure it out. A proper schematic would help...
Yes. But when I add 24+ att VCC I get 24+ at the input and output. Also if I try to add 5+V at input the output is still 24+V. I tried at a single LM 358 to add 24+ at VCC and GND at VCC-, then i didnt get 24 volt on the output and input...
I have no spare quad op amp so i dont know if this i right...
Southpark:
The diagram you provided isn't a 'beginners' one.If you're a beginner, as you mentioned, then start with a single LM324, and do some basic tests and exercises, such as to construct a non-inverting op-amp with a gain of approximately 2.
Also, note that single supply is being used here. So the input to the operational amplifier circuit with need to be appropriately biased (DC-biased).
Also - in your diagram --- the 4th op-amp component isn't being used. So look up information (online) that tells you what to do with unused op-amps ----- to ensure that its inputs aren't floating, and may become sources of noise due to floating inputs.
I know this isnt a beginners one. I have som experience with theoretic filter and opamp, but have never solder one.
Yes, its DC voltage used.
I will look up information about the 4th op-amp. Thank you for that.
MarkT:
They are DC biased if connected to current loop inputs, 250 ohm load resistors means the signals between
+1 and +5V at the inputs. The opamps in question are happy with signals down to the 0V rail anyway, its clear
from the filter time-constants and input circuit and 24V supply this is not an AC amplifier!
Its a DC amplifier/filter. But the input is a 4-20mA signal. Its filtering noice.
Southpark:
When I see labels saying 'filterinn' ....... then my assumption is AC. It might be the wrong assumption...... but AC is what I assume to begin with. Not necessarily an 'AC amplifier'. But a filter, involving AC.
Its a DC amplifier/filter. But the input is a 4-20mA signal. Its filtering noice.
The top signal path worries me - I would have expected the filter part of it to be a Sallen/Key stage like this:
but you have a buffer stage in the middle of that, which will change the response curve (I've never
seen that topology).
The input buffers aren't really necessary as the 250 ohm resistor lowers the impedance to well below the
filters' 15k and 22k input resistors.
So I think you can remove 3 opamp buffer stages and implement everything with a single quad opamp,
one opamp for Sallen/Key filter, two for the offset/gain adjust, and a single opamp buffering the output
of the second signal path.
The gain-offset circuit can be rearranged and done with a single opamp too, and it should ideally have a
capacitor to reduce noise across the voltage divider output, given the high resistor values - large
resistors have more voltage noise and this circuit is after the low pass filter so it makes broadband noise.
Perhaps gain/offset could be before LPF for reduced noise output?
Found a spare LM324 and noticed the spare part didn't act the same as the first one. So I conclude that the first one was blown. Thank you.
pederw:
Actually the only thing i need to know is if someone have a spare LM324. Add 24+V att VCC and GND att VCC-, then measure over the other pins, do you get 24+V or not?
Connecting an OpAmp to power with its inputs disconnected (floating) is generally a bad idea. That's why, when designing circuits, unused OpAmps (they normally come in dual packages) will normally be wired as unity gain voltage follower with the other input connected to GND, Vcc or (more commonly) a mid point through a voltage divider.