# Scaling 0-10VDC to 1-5VDC?

#### boulderjoe

Joined Nov 21, 2011
5
Hi, I've been lurking for a while in here but can't seem to find an elegant combination for what I'm trying to do.

I have a 0-10VDC output from an instrument I'd like to interface to a 1-5VDC readout. I could use a simple voltage divider if I could use 0-5V, but I'm getting hung up combining the scaling with the offset. Can I use an opamp to add 1V and scale my signal to a 0-4V scale?

Any suggestions?

Thanks, Joe

#### thatoneguy

Joined Feb 19, 2009
6,359
How much current did you need? Is this for Analog to Digital conversion or other purpose?

What is the accuracy required?

One method that comes to mind is a trans-conductance amplifier, so the output current scales with the input voltage.

Put the output current through a precision resistor to produce a 1V-5V voltage across that resistor based on output current, which is directly related to input voltage. Thinking instrumentation 4-20mA through a 250 Ohm resistor will give the 1-5V output.

However, this depends on what you will be using the 1-4V for, if more than a few mA are required, that solution won't work.

#### boulderjoe

Joined Nov 21, 2011
5
Thanks for the quick reply. I don't think current is an issue. It's for A-D purposes. A pressure gauge with a 0-10V analog signal going to a different manufacturer's pressure readout, with a 1-5V analog input. It then just converts the analog signal to a digital display.

The gauge is 0-1000Torr scaled to 0-10V, so mV accuracy is about all that's needed (0.1 Torr)

#### thatoneguy

Joined Feb 19, 2009
6,359
How much experience do you have with electronics?

There is an IC built specifically for this: XTR110

#### SgtWookie

Joined Jul 17, 2007
22,221
Thanks, Ron_H - I figured it could be done with fewer parts, but I don't seem to be firing on all cylinders for the last week or so.

It would be helpful to our OP and others if you provided details how to "fine tune"/calibrate the circuit in order to compensate for component tolerances.

#### SgtWookie

Joined Jul 17, 2007
22,221
@strantor: you weren't kidding about needing money to burn, I can't believe that guy is $300. Considering how much it would cost to pay an engineer to design a functionally equivalent general-purpose device and then have it built,$300 for an off-the-shelf device is a deal!

#### Ron H

Joined Apr 14, 2005
7,014
Thanks, Ron_H - I figured it could be done with fewer parts, but I don't seem to be firing on all cylinders for the last week or so.

It would be helpful to our OP and others if you provided details how to "fine tune"/calibrate the circuit in order to compensate for component tolerances.
There's always a gotcha.
As I think you realize, all the resistors interact. That is the advantage of your circuit.
I provided the simpler circuit partly as an intellectual exercise, and partly in case the accuracy of 1% resistors would be adequate. I realize that I did not put 1% resistors in the schematic. The ratios of the 3 resistors need to remain as shown on the schematic when picking values.

#### SgtWookie

Joined Jul 17, 2007
22,221
Yep, I realize that.
But, here are some values our OP could use to either hit or get very close to 129.17 Ohms:
Rich (BB code):
E96 resistance values for series/parallel combinations to get 129.17 Ohms
25 combinations found                                   % of
R1             R2          Total R   Error
-------        -------      --------   -----
1)      137.00 ||     2260.00 =      129.17,  0.000%
2)      150.00 ||      931.00 =      129.19,  0.012%
3)       38.30  +       90.90 =      129.20,  0.023%
4)       31.60  +       97.60 =      129.20,  0.023%
5)       16.20  +      113.00 =      129.20,  0.023%
6)      200.00 ||      365.00 =      129.20,  0.026%
7)      133.00 ||     4530.00 =      129.21,  0.028%
8)      169.00 ||      549.00 =      129.22,  0.040%
Of course, we don't know what kind of accuracy they require - and if they were reading it using a uC, they could just calibrate out errors via the software.

#### thatoneguy

Joined Feb 19, 2009
6,359
Thanks everyone! I've got a handle on it now.

@strantor: you weren't kidding about needing money to burn, I can't believe that guy is $300. To be fair, that device can operate in current in/voltage out, voltage in/voltage out, or voltage in/current out modes, all with 180V of isolation, so there is quite a bit more design that has gone into it, as well as parts, not to mention$20 worth of dust/grease/moistureproof enclosure for industrial environment (which I assumed you were in when I suggested the 4mA-20mA). Standards and all of that.

If this is in an industrial setting, be sure to put the schematic inside the enclosure and the function of the unit on the outside of the enclosure for anybody that may need to look at it in the future, please! Possibly offer buffered 0-10V and 1-5V outputs of the enclosure as well, in the event that pressure reading is wanted for another use later down the road.

#### strantor

Joined Oct 3, 2010
5,508
If this is in an industrial setting, be sure to put the schematic inside the enclosure and the function of the unit on the outside of the enclosure for anybody that may need to look at it in the future, please!
Yes, nothing more frustrating than coming upon some unknown, unlabeled beast whilst troubleshooting a machine and have to dissect the thing just to understand what it is/what it does/why its there before you can move on. For your application, the function of the board would be fairly obvious (a signal conditioner), but not the specifics of it. Things like this save downtime, and downtime always comes when you least want it.

#### Ron H

Joined Apr 14, 2005
7,014
Yep, I realize that.
But, here are some values our OP could use to either hit or get very close to 129.17 Ohms:
Rich (BB code):
E96 resistance values for series/parallel combinations to get 129.17 Ohms
25 combinations found                                   % of
R1             R2          Total R   Error
-------        -------      --------   -----
1)      137.00 ||     2260.00 =      129.17,  0.000%
2)      150.00 ||      931.00 =      129.19,  0.012%
3)       38.30  +       90.90 =      129.20,  0.023%
4)       31.60  +       97.60 =      129.20,  0.023%
5)       16.20  +      113.00 =      129.20,  0.023%
6)      200.00 ||      365.00 =      129.20,  0.026%
7)      133.00 ||     4530.00 =      129.21,  0.028%
8)      169.00 ||      549.00 =      129.22,  0.040%
Of course, we don't know what kind of accuracy they require - and if they were reading it using a uC, they could just calibrate out errors via the software.
And 620k is not a standard value, although 619k is.