kcampbell
Member
Hello,
I have a 2 wire, 0-10vdc output, self (not loop) powered current transducer from NK Technologies that's giving me incorrect values when I have it connected to any of the analog inputs on my SCADAPack 350 RTU. The inputs are all set to voltage mode.
With the transducer set in the 0-10 Amp range, I can get correct readings if I use just my multimeter. For example, a 60 watt lightbulb at 120 vac gives me just under 0.5 volts DC. But the same reading via the PLC gives me 0.42 volts DC.
The problem is, I think, that the NK transducer needs a minimum of 100K Ohm resistance across it's output at the measurement end, preferably 1 Meg Ohm... and the analog inputs on the PLC already seem to have about 20K Ohm built in, as measured with my multimeter. So any resistance I add between the analog input pin and ground is effectively decreasing the resistance as per the resistors-in-parallel calculation. The multimeter has a built in impedance of about 20 Megohm, which explains why the readings are as expected when I have the transducer connected to just the multimeter.
Any suggestions on how to deal with this would be appreaciated.
Datasheet for the NK transducer here, part# AT1-010-000:
http://nktechnologies.com/current-transducers/datasheet/at-current-transducers.pdf
Regards,
Ken Campbell
I have a 2 wire, 0-10vdc output, self (not loop) powered current transducer from NK Technologies that's giving me incorrect values when I have it connected to any of the analog inputs on my SCADAPack 350 RTU. The inputs are all set to voltage mode.
With the transducer set in the 0-10 Amp range, I can get correct readings if I use just my multimeter. For example, a 60 watt lightbulb at 120 vac gives me just under 0.5 volts DC. But the same reading via the PLC gives me 0.42 volts DC.
The problem is, I think, that the NK transducer needs a minimum of 100K Ohm resistance across it's output at the measurement end, preferably 1 Meg Ohm... and the analog inputs on the PLC already seem to have about 20K Ohm built in, as measured with my multimeter. So any resistance I add between the analog input pin and ground is effectively decreasing the resistance as per the resistors-in-parallel calculation. The multimeter has a built in impedance of about 20 Megohm, which explains why the readings are as expected when I have the transducer connected to just the multimeter.
Any suggestions on how to deal with this would be appreaciated.
Datasheet for the NK transducer here, part# AT1-010-000:
http://nktechnologies.com/current-transducers/datasheet/at-current-transducers.pdf
Regards,
Ken Campbell
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