fireattack
Member
Hi everyone,
I have a course doing lab with AB's controller and it's very fun. However, in today's lab, we were working with the "DC output" module, which makes me very confused.
My equipment is a logix5550 controller with lots of modules, the one we cared here is the so-called DC-output: 1756-OB8.
My lab assignment today is to connect a pair of output from the DC output module to a relay's coil along with a 24VDC, and another circuit is relay's contact connected to a motor (and its own power for sure, a 14VDC). The input of my controller is a built-in switch (already connected to another module (IA16) with power) and using ladder logic to connect the input and the actuator (the dc output) like:
|----] [-----( )----|
IN-0 OUT-0
The supposed result is very simple: if you close the switch, the motor will run and vice versa.
My instructor said, the DC output here is just like a swtich- if your ladder logic give it a bit of 1, it closed; otherwise it's open. But it sounds very wrong to me. Because if I use the multimeter to check the resistance of two pin of my DC output, it always shows "open loop" no matter if my switch is open or closed - that's not what a switch does. I asked him, he has no idea as well.
So my questions are:
1. What exactly did it the DC output do? The manual from AB looks too complicated to me, but It said it's a digital output? So it's only have two status? like high voltage and low voltage or what? I used multimeter to test it with R/V/A but didn't see any difference between two status, why?
2. If it's a digital output, why it's name is "DC" output?.. this confused me so much.
3. Why we need to connect an 24VDC to the output module? I mean if it really works as a switch, sure. But I hardly believe it: if so what's the difference between a DC output and a relay output then.. (we use reply output mostly before)
3. Will the two circuits I mentioned above actually work? My motor did rotate for once, but sometimes when I open the switch and closed again, it failed mysteriously and the instructor didn't know why either.
I know I may be lack of basic electric knowledge since I'm actually from mechanical engineering. Sorry about that!
I have a course doing lab with AB's controller and it's very fun. However, in today's lab, we were working with the "DC output" module, which makes me very confused.
My equipment is a logix5550 controller with lots of modules, the one we cared here is the so-called DC-output: 1756-OB8.
My lab assignment today is to connect a pair of output from the DC output module to a relay's coil along with a 24VDC, and another circuit is relay's contact connected to a motor (and its own power for sure, a 14VDC). The input of my controller is a built-in switch (already connected to another module (IA16) with power) and using ladder logic to connect the input and the actuator (the dc output) like:
|----] [-----( )----|
IN-0 OUT-0
The supposed result is very simple: if you close the switch, the motor will run and vice versa.
My instructor said, the DC output here is just like a swtich- if your ladder logic give it a bit of 1, it closed; otherwise it's open. But it sounds very wrong to me. Because if I use the multimeter to check the resistance of two pin of my DC output, it always shows "open loop" no matter if my switch is open or closed - that's not what a switch does. I asked him, he has no idea as well.
So my questions are:
1. What exactly did it the DC output do? The manual from AB looks too complicated to me, but It said it's a digital output? So it's only have two status? like high voltage and low voltage or what? I used multimeter to test it with R/V/A but didn't see any difference between two status, why?
2. If it's a digital output, why it's name is "DC" output?.. this confused me so much.
3. Why we need to connect an 24VDC to the output module? I mean if it really works as a switch, sure. But I hardly believe it: if so what's the difference between a DC output and a relay output then.. (we use reply output mostly before)
3. Will the two circuits I mentioned above actually work? My motor did rotate for once, but sometimes when I open the switch and closed again, it failed mysteriously and the instructor didn't know why either.
I know I may be lack of basic electric knowledge since I'm actually from mechanical engineering. Sorry about that!
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