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justwhy2003

0-10v input using 0-5v

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hello again. im considering puchasing a unitronics jaz range micro plc with analog input 0-10 volts. however i am usin a pressure transmitter giving 0-5 vols out. is it normally acceptable to use the lower half of the 0-10v scale just for 0-5 volts or will i need to amplify the signal in in some manner. also, has anyone any experience with these range of micro plcs and could they provide any good/bad feedback before i dedicate money to one?? thanks justwhy2003 oh forgot to say, there is also a 4-20mA option for the analogue input, would the addidion of a 250 ohm resistor be a more appropriate solution and how acceectable and wide used is this method in industry? thanks

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As long as you can live with half the full-scale resolution, you're fine. Not sure about the 250 ohm resistor, though. Would be interested to hear of others do this

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see the below link for a singal conditioner that fits your needs. http://www.api-usa.com/signalconditioners_dc_input.php

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There is probably not much to be gained by using an amplifier. Chances are your resolution will be adequate and any intermediate amplifier or signal conditoner is just going to amplify any inaccuracies in your transducer as well, plus add in its own. Just go with the 5V and scale accordingly.

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Use the 0-5Vdc input with your existing 0-10Vdc analog input. As mentioned, you only get half the resolution, but it is highly unlikely that doubling the resolution with an signal conditioner preamp will improve your process enough to give you any reasonable payback on a signal conditioner, and it would add a potential failure point. You'll have to scale your input for twice what you expect. If the 0-5V represents 0-2,000 gallons, then you need to scale your input 0-4,000 gallons for the 0-10 input range, because the 5V will only ever reach half of whatever your scale is. Don't mess with the 250 ohm resistor. The 250 ohm resistor is needed only with milliamp current signals (which you don't have), not with voltage signals, because the analog input is voltage sensitive, not current sensitive. For current loops, the current runs through the resistor, creates a voltage drop of 1.0 to 5.0 volts (by Ohm's Law E = IR) and the analog input is happy. For a 0-10V scale, a 500 ohm resistor would give a 2.0 to 10.0 volt drop. 4-20mA is used because it is fairly noise resistant and can be run long distances, like a mile, which a consideration in an oil refinery or a steel mill that covers an area of square miles. Since it is a current signal, it is the same at all points in the loop, unlike a voltage signal which fades (voltage drop) due to resistances in the wiring. Dan

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justwhy2003, It appears the full scale resolution is 10 bit (1024) half of that would be 512. If this fits your project then go for it!

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thanks. im presuming that the pressure transduce will require a seperate 5 volt supply while the 0-5 variable volt input will be fed directly into the analog input terminals?

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Probably not, most industrial sensors use 24vdc for a power supply. Check the manufacturer's documentation, you can not presume what the power supply requirements are. I would also not "just go with it". The 0-5V into a 0-10V input gives you only 512 bits. That resolution usually sucks unless your application really can deal with it. You'll have to calculate the accuracies and see. I would investigate buying the pressure transmitter with a 4-20mA output and use your 4-20mA input into the PLC. You still need to check the accuracy and resolution of that as well before you do so.

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