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Open analog input condition - SMC-G2-18V25

SMC-G2-18V25 p/n 1366

I have programmed my SMC-G2-18V25 to output 0 to 24 VDC on an analog input of 0 to 3 VDC (a1 & -). This works well even with the high pitch hum from the switch mode power supply. However, when the input circuit is opened the output drives to 14 VDC. I need the output to drop to 0 VDC on open analog input. Any suggestions on settings, please?


When the SMC G2 is in “Analog” input mode, it generally triggers the “Required channel invalid” error if an analog input is not connected. Can you post more details about what you are using for your 0-3V analog input, and include some pictures of your setup that show all of your connections? Also, could you post a copy of your SMC G2 settings file? You can save a copy of your settings file form the “File” drop-down menu of the Simple Motor Control Center G2 software while the controller is connected.


Hi Brandon,
We use a process controller with a floating DC analog output. The driven device is connected to a different 24 VDC switched mod power supply. The controls and driven devices are proprietary but here is the photo of the SMC G2 18V25 board prior to mounting and labeling.
Pololu 18v25 G2 smc_settings.txt (2.1 KB)

Thank you for the additional information. You might consider adding a 100k pull-down resistor so the signal goes low instead of floating.


Hi Brandon,

I believe we are using different meanings of floating…the driver functions quite well with the isolated 0 to 3 volt signal (= 0 to 23.5 Volt output). The issue is a broken analog wire or the process controller being pulled from its socket during service. Are you suggesting a resistor across A1 to (-)?


Yes, you could put the pull-down resistor across A1 and - pins. This would cause the SMC G2 to read 0V if your 0-3V signal is removed, and it should generally not interfere with the analog signal when it is driven.


Thank you. Is there a firmware setting to ignore the “Required channel invalid” error?

The “Ignore pot disconnect” option in the “Advanced settings” tab of the Simple Motor Control Center G2 disables the disconnect detection for analog channels. The analog channel will still be considered invalid if the voltage goes out of the acceptable range specified by the “Error min” and “Error max” parameters for that channel.