hi All

Can you please kindly advise how to check analogue output if its working in 4-20mA mode?
my idea is to connect 250 ohm resistor to the AO output, set drive to hand, disconnect motor, set ref to 100 percent and check if the voltage at full 20 mA is 5 V. Is that correct?
Any other ideas?
Please share you knowledge

 

If your AO is sending 1-5 VDC and you want to measure 4-20mA, then 250 ohm resistor connected in shunt will be a good choice. But if you are already already sending 4-20mA in the output, no need to put a resistor. You can use multimeter in series with your field instrument to measure the current (set your meter to current port). But if you suspect that you are sending voltage instead of current, you can connect the multimeter directly to the output terminals to measure if it is indeed in voltage mode. The voltage should change when you change command. Current mode should not change the voltage in any way.

 

If your AO is sending 1-5 VDC and you want to measure 4-20mA, then 250 ohm resistor connected in shunt will be a good choice. But if you are already already sending 4-20mA in the output, no need to put a resistor. You can use multimeter in series with your field instrument to measure the current (set your meter to current port). But if you suspect that you are sending voltage instead of current, you can connect the multimeter directly to the output terminals to measure if it is indeed in voltage mode. The voltage should change when you change command. Current mode should not change the voltage in any way.

thanks for your kind and very practical advice.
Can you please help me with the remaining questions:
1: If the AO is in the current mode does it mean that the resistance of the field must be exactly 250 Ohms? What if it mismatches by a lot or is near 0.
2: Is that possible that the field wiring having issues might cause the AO to stop sending any current? For example if the field wiring resistance is too small would 20mA be sent as maximum value or would it revert to sending 4 mA value
3: if we have AO in 4-20 mA (as oppose to 0-20mA) - it would be practical to see at least 4 mA which means that on my 250 Ohms resistor i will see exaclty 1 Volt? If i dont see that value that AO is not working in the current mode.
4: is AO galvanically isolated from the field so there is nothing that field can do to brake AO output and if it stops working it is VFD issue?

Kind Regards

 

Hi! Replying to your questions (with questions) -

1: If the AO is in the current mode does it mean that the resistance of the field must be exactly 250 Ohms? What if it mismatches by a lot or is near 0. - How are you measuring the resistance? Is it with power? Why do you want to check the resistance? Check for voltage and current instead. How much voltage do you get? How much current?

2: Is that possible that the field wiring having issues might cause the AO to stop sending any current? For example if the field wiring resistance is too small would 20mA be sent as maximum value or would it revert to sending 4 mA value - Compare what voltage you get when the field device is connected to the terminal and when you disconnect it. Maybe the device is shorting the line.

3: if we have AO in 4-20 mA (as oppose to 0-20mA) - it would be practical to see at least 4 mA which means that on my 250 Ohms resistor i will see exaclty 1 Volt? If i dont see that value that AO is not working in the current mode. - Again, if you are already in current mode and you want to put a resistor, your voltage is unpredictable. You cannot make the output go to voltage mode if you are in current mode. But you can make the voltage mode to become current mode when you apply resistor,

4: is AO galvanically isolated from the field so there is nothing that field can do to brake AO output and if it stops working it is VFD issue? - Are you asking a question on your first sentence or is it a statement? I have no clue about your AO card if galvanically isolated or not (and you did not even identify). For most AI/AO cards, they will not break even if you short them out.

What exactly do you want to achieve here?

 

1. Analog output
On page 170 The Sinamics G120 manual at this link
file:///C:/Users/danw/Downloads/G120C_op_instr_0917_en-US.pdf
it says that the analog output can be configured for either 0-20mA or 0-10Vdc or 4-20mA

It is not clear which is the default setting because the states that "The inverter offers a series of default settings," I agree that there is a series of settings to choose from, but there can only be one 'default' ("meaning as it comes from the factory") setting.

More importantly, the manual discloses that

- you must to associate the analog output setting with a CO, Connector Output, whatever that is (I've never seen a Sinimics drive before, I'm just looking at the manual.)

- the analog output function can be defined and there's list of choices on page 171.

- it appears that there is only one (+) terminal, terminal 12, for the analog output. I do not have a clue where the AO(-) terminal is supposed to be. Physically connecting an analog output that needs two terminals, when only one terminal is shown, is the challenge here.

It might pay to check out the manual for AO configuration.

2. You don't need a 250 Ohm resistor to check either current output or voltage output. A 250 Ohm resistor is never used a DC voltage output. For current readings, use the DVM's milliamp scale. For voltage, use the DVM's DC volts scale.