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Cant get my voltage in CIOx and EIOx below 1 V

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#1 alberto

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Posted 03 May 2013 - 03:40 PM

Hello, I want to control some SSR (KYOTTO KD20C40AX) using a Labjack U3-HV. I have one SSR connected to VS and CIO2. On Labview im using LJUDeGetS to swith my port 16 between LJ_ioPUT_DIGITAL_BIT and LJ_ioGET_DIGITAL_BIT. When I use LJ_ioPUT_DIGITAL_BIT I get 3.71V acrros the control inputs of the SSR and when I use LJ_ioGET_DIGITAL_BIT the voltage across the control inputs is 1.01V. The DataSheet of the relay says in order to turn the SSR off max voltage is 0, do I need to to put a resistance between the Labjack and the SSR? Also, how can I configure the digital lines as output-low in Labview? Thank you

#2 LabJack Support

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Posted 06 May 2013 - 09:43 AM

When you do PUT_DIGITAL_BIT, you pass Value=0 for output-low and Value=1 for output-high.

The datasheet for the KD20C40AX specifies a turn off voltage of <1.0V and a turn-on voltage of >4V. You are very close to those numbers, so is the SSR turning on/off properly?


The SSR likely has a resistor in series with a diode. Enough current has pass through the diode to create enough light to activate the optotransistor on the output side. If you

We use that relay all the time. We have noticed strange voltages at times across the control inputs (likely due to leakage currents through the diode), but have not had any trouble with the SSR not turning on/off as specified. In the figure at the lower-right of the SSR datasheet (which seems to be mislabeled), I see that the actual turn-on voltage is typically 1.8-2.1V across temperature, and the turn-off is 1.3-1.8V.

Also see "Optional Configuration" and you might try adding a 27k pull-up to see if that changes things:


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