analog invert

[ahuat 0]

Hello All, I need to invert analog input from 4-20mA into the reverse 20-4mA, i think some signal processor like K3NX or K3GN can do it, but the price is quite expensive. Does anybody has experience for doing the inverse in cheaper solution? Thanks in advance. ahuat

[Tigamaroo1999 0]

You could invert the signal which seems quite difficult. Or, you could just modify your programming to accomodate this. All you would have to do to make this happen in the world of programming is subtract the maximum from whatever your signal should be: Example: Max input = 4000 = 20mA Your input = 1000 = 8mA (Max - Yours) = Analog Input 4000- 1000 = 3000 Analog input = 3000 = 16mA If your input were 0, you would get Max output and vice versa. I hope that made some sort of sense...it's late in the week. Tig

[ahuat 0]

Thank you TigaMaroo1999, i haven't use any PLC yet, because the modules are relatively expensive, even the price for K3GN is too expensive, i need a 'simple' converter to invert the signal, if someone knows about it, pls inform. regards ahuat

[Sleepy Wombat 27]

What are you doing with the signal ? A little more info might get a few more answers .

[ahuat 0]

i want to run an variable speed motor for a pump, the variable speed driver module is in a package with the pump so i can not change it. i also have to connect a pressure transmitter, with 4-20mA ( without invert option ) to the variable speed driver. now i can not do that because the pressure transmitter output will follow the water pressure. 0 bar means 4mA and 10 bar means 20mA, while the variable speed driver also can not invert the analog input signal, that is mean 4mA means 40% of the speed and 20mA means 100% of the speed. what i am trying is i am looking for a 'cheap' solution to invert the signal, so if the pressure transmitter give 4mA the output will be 20mA and if the signal is 20mA the output is 4mA. anybody has suggestion? thanks in advance. ahuat

[Guest Guest]

Don't you have gain/bias settings on the drive ? Then you could set gain (freq at max input) at 0% and bias (freq at min input) at 100 %.

[PdL 71]

Sorry - forgot to log in

[Sleepy Wombat 27]

I agree with PDL, if still not an option, seriously, how much more is it for a presure sensor that can invert the output... other inline convertors could be around $400 at least...

[ahuat 0]

no, it's not possible to adjust the bias, .... the drive gives very few features only... anyway.... thanks for the replies .... best regards ahuat

[moosty 0]

May be it is possible to desiqn an electronic circuit with two op-amps, possibly with a few resistors and an op-amp IC containing at least two op-amps inside. I will try to design one. One op-amp will invert the signal, and one will be designed as current injector.

[ahuat 0]

it sounds interesting..., i hope the design is stable enough, i already tried to find inverted pressure transmitter, but seems it's difficult to find it locally..., hopefully you are success with your design. regards, ahuat

[ahuat 0]

Finally, i decide to use E5CK with analog output E53-C4R4, it has a reverse operation and i can get it under USD 200, ahuat

[JaspaJami 0]

Old post that i use, hopefully it doesnt matter. I have basically exactly same problem.

Im using 4-20mA PT100 transmitter, measures tempareture 0-50c. In 0c output is 4mA and in 50c output is 20mA, but i need to invert that. And i havent seen any PT100 transmitters with inverted output.

Drive that i use for the motor is Altivar 11, manual: https://stevenengineering.com/tech_support/PDFs/45A11UG.pdf

If i understand correctly drive itself doesnt support inverting input. And i dont understand exacty this bias/gain talking that was earlier that can i do it with that trick?