defcon.klaxon
Lifetime Supporting Member
Hi guys,
I'm noticing something strange in my ControlLogix L72 when I call a VFD to run, and I'm not sure if it's a coding/config problem on the output card or if it's a VFD issue. Here's the lowdown:
PLC - ControlLogix 1756-L72
Analog Output Card - 1756-OF8
Output Range - 0 to 20mA
Output High Scale: 20.0 mA
Output High Engineering: 20000.0
Output Low Scale: 4.0 mA
Output Low Engineering: 4000.0
Output High Clamp - 21000
Output Low Clamp - 3200
Disable All Alarms - Checked
VFD - Allen Bradley SpeedFlex 525
Parameters - Unknown, they were configured by the panel builder so if there's something I should look at, let me know.
What happens is, if the VFD is in Auto but I'm not calling the VFD to run, the analog output value is 4000.0; makes sense, since it's a 4-20mA output. However, if I call the VFD to run, the output value immediately goes to -1.0. If I force the output (4000.0-20000.0) the speed responds properly, strangely.
The way my code works, is that the speed setpoint is 0-100%, and that's scaled to 4000-20000 and then that value is moved to the output tag. Originally I had the speed setpoint as a DINT; if I change it to a REAL, I get -1.$ and the output goes full scale; however, if I force it it does behave as intended.
So I'm not sure if this is a VFD issue or an output config issue or a code issue. My outputs seem to be working just fine for the GE VFDs we also have so I'm not sure what to be looking for. Any thoughts on what could be causing this? I am cautiously optimistic it isn't my code or config, but not sure what would cause this if it is indeed VFD related.
I'm noticing something strange in my ControlLogix L72 when I call a VFD to run, and I'm not sure if it's a coding/config problem on the output card or if it's a VFD issue. Here's the lowdown:
PLC - ControlLogix 1756-L72
Analog Output Card - 1756-OF8
Output Range - 0 to 20mA
Output High Scale: 20.0 mA
Output High Engineering: 20000.0
Output Low Scale: 4.0 mA
Output Low Engineering: 4000.0
Output High Clamp - 21000
Output Low Clamp - 3200
Disable All Alarms - Checked
VFD - Allen Bradley SpeedFlex 525
Parameters - Unknown, they were configured by the panel builder so if there's something I should look at, let me know.
What happens is, if the VFD is in Auto but I'm not calling the VFD to run, the analog output value is 4000.0; makes sense, since it's a 4-20mA output. However, if I call the VFD to run, the output value immediately goes to -1.0. If I force the output (4000.0-20000.0) the speed responds properly, strangely.
The way my code works, is that the speed setpoint is 0-100%, and that's scaled to 4000-20000 and then that value is moved to the output tag. Originally I had the speed setpoint as a DINT; if I change it to a REAL, I get -1.$ and the output goes full scale; however, if I force it it does behave as intended.
So I'm not sure if this is a VFD issue or an output config issue or a code issue. My outputs seem to be working just fine for the GE VFDs we also have so I'm not sure what to be looking for. Any thoughts on what could be causing this? I am cautiously optimistic it isn't my code or config, but not sure what would cause this if it is indeed VFD related.
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