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I have an Allen Bradley ControlLogix 11756-L72S PLC with a 1734-OE2V 2-Point Analog Output card connected to a SMC pressure regulator that takes a 0-10 V input signal to set the pressure setpoint.

I want to test that the loop is scaled correctly. I'm thinking that I'll enter the setpoint at the HMI and verify the voltage at the input. So with a setpoint of zero (0) psig I would expect 0 V at the input and with a setpoint of 75 psig I would expect 10 V the input, which would then be configured at the device to correspond to 75 psig.

Is this a good way to test analog output scaling? Is there anything I'm missing?

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  • \$\begingroup\$ Is the regulator supposed to give 75 psi at 10 V? Your post doesn't make it clear and the SMC link has several different versions. \$\endgroup\$
    – Transistor
    Dec 2, 2019 at 21:35
  • \$\begingroup\$ @Transistor It's supposed to give the max pressure at 10 V. The specific max pressure of 75 psig is configurable at the device. Hope this clarifies! \$\endgroup\$
    – dikuw
    Dec 2, 2019 at 22:36
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    \$\begingroup\$ This pressure regulator has a black wire for monitor output, could check that to the blue wire (common.) The datasheet gives little for specifications. I'd check it at 0%, 50%, and 100%. Add a 0.1µF capacitor across the white and blue if noise is suspected. \$\endgroup\$
    – rdtsc
    Dec 2, 2019 at 22:48

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I'd say you've got the right idea.

Make sure the HMI user setpoint scales correctly in the PLC. In other words, if the HMI reads 0 to 75 PSIG, you may want it to scale as an INT from 0 to 100 in the PLC. Verify that scaling is correct.

Then check that the INT is scaling the analog output properly. Force the INT from 0 to 100 and make sure your multimeter is reading 0 V to 10 V. I'd do some quick steps of 10 for 1 V increments.

Power up your regulator and set the min and max pressure points. Looks like 0 V corresponds to the min and 10 V corresponds to the max from the manual. I'd also connect that monitor to an analog input. Useful for developing a loss of pressure alarm.

Finally, you've got to check the whole loop. Punch in [0, 25, 50, 75] PSIG on the HMI, read a [0, 33, 67, 100] on the INT, getting [0, 3.3, 6.7, 10] V out, and read [0, 25, 50, 75] PSIG on the regulator. The regulator pressure may not be perfectly linear, [0, 24, 48, 72] PSIG, in which case you'd need to decide if the error is acceptable or if some tweaking is required.

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  • \$\begingroup\$ great answer - thanks! \$\endgroup\$
    – dikuw
    Dec 3, 2019 at 15:57

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