Hi.
I'm using a NI USB-6009 data acquisition card to send a signal to a proportional pressure controller which varies the supply pressure to a pneumatic system. Unfortunately, the pressure controller requires a 0-10V analogue control signal and the 6009 can only do 0-5V (very low current).
So I thought I would build a little circuit with a gain of 2 to amplify the signal. The 741 op-amp is powered by a 24V DC supply. 24V is a little on the high side for the op-amp but I have this supply already built in and (using a lab bench supply) the circuit works exactly the same at 12 and 18V. See links below (or attachments for pics)
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Bascially, with input voltages from 5 down to 2 volts, the circuit behaves perfectly. The output is just the input multiplied by two.
However, the output never goes below 3.9 (ish) volts, no matter what the input voltage is.
Can anyone suggest a solution (or know where else to ask)? I really need to be able to control my output within the range of 1-10V. Is this a featurewith the op-amp? If so, is there a more suitable one out there that can handle low input voltages?
Many thanks. J