eric,
i saw your simulation.. but this circuit did not satisfied the my another condition... for zero input output should be 4mA

hi,
To get 4mA for 0v input [330R at the bridge], you need to apply a offset voltage at the U1/2 inputs so that Vout=1 v for a 330R value]
So that Vinp to the V2I converter is 1V thru 5V, for 4mA to 20mA output, which is a common method.
E

 

hi,
To get 4mA for 0v input [330R at the bridge], you need to apply a offset voltage at the U1/2 inputs so that Vout=1 v for a 330R value]
So that Vinp to the V2I converter is 1V thru 5V, for 4mA to 20mA output, which is a common method.
E

can you briefly explain it..? also is there anyoption to modified in U4 opamp side ( V-i converter circuit) to achive 4mA at zero output

 

hi,
There is an alternative method.
Adding a 2N3819 constant current source, to offset the Iout to4mA for a Vin of 0v.
Note that Vin will be from 0V thru 4V [ reduce the IA Gain]
E

 

hi,
There is an alternative method.
Adding a 2N3819 constant current source, to offset the Iout to4mA for a Vin of 0v.
Note that Vin will be from 0V thru 4V [ reduce the IA Gain]
E
View attachment 153145

okay eric... first i collect the components , then do it practically and will post my readings

 

hi,
There is an alternative method.
Adding a 2N3819 constant current source, to offset the Iout to4mA for a Vin of 0v.
Note that Vin will be from 0V thru 4V [ reduce the IA Gain]
E
View attachment 153145

hi eric,
By same is there any another option to limit the 20mA current output at U4 opamp side( V-I converter). i will try zener diode method but i would be better if we modified it on V-I converter side. is there any possible...

 

hi,
This is the simplest circuit that will work as required.
E
EDIT:
Added a circuit showing the Trim Pots and the variation in the 330R

 

hi,
This is the simplest circuit that will work as required.
E
EDIT:
Added a circuit showing the Trim Pots and the variation in the 330R

dear eric,
i can't able to understand your last post?

 

hi rajit,
If you mean the simulation.?
I set the bridge R14 resistor to step in value from 330R to 331R in 0.1R increments.
For each increment in R14, the plot shows the Iout current from 4mA thru 20mA [limiting close to 20mA]

R18 is adjusted for Zero Vout when R14 =330R.

E

 

hi rajit,
If you mean the simulation.?
I set the bridge R14 resistor to step in value from 330R to 331R in 0.1R increments.
For each increment in R14, the plot shows the Iout current from 4mA thru 20mA [limiting close to 20mA]

R18 is adjusted for Zero Vout when R14 =330R.

E

dear eric,
i have to change the R7 resistor value for 330 to 330.7 not in R14 and may i know the use of 47micro and 100n f capacitor?
is that any equivalent JFET is available to replace J1(2N3819)

 

hi,
It is a simple as swapping R7 and R14 on the bridge over, [also moving R18] this sim shows the result.
What type of n JFET's are you able to buy in your area.?

The 47uF and 100uF are required for power supply decoupling.
E

 

hi,
It is a simple as swapping R7 and R14 on the bridge over, [also moving R18] this sim shows the result.
What type of n JFET's are you able to buy in your area.?

The 47uF and 100uF are required for power supply decoupling.
E

okay eric.
i asked for same spec of J1. but there is not available exact spec? still now i search for same spec..

 

hi j,
This is the 2N3819 datasheet.
E

EDIT:
Check this link for equivalent.
https://english.electronica-pt.com/components-cross-reference?ref=2N3819

 

hi j,
This is the 2N3819 datasheet.
E

yes eric i saw it.. i asked the same spec 25v, 2-20mA

 

hi j,
This is the 2N3819 datasheet.
E

EDIT:
Check this link for equivalent.
https://english.electronica-pt.com/components-cross-reference?ref=2N3819[/QUO

dear eric,
i looking to the equivalent for j1.
i will inform you the availability of alternative components (BF244, BF245, BFS72, 2N3823)

 

Reinventing the wheel might be fun but the XTR105 is your man- modules galore using this ic available from leading auction sites for $10. Less than the price of a decent INA!


Here is a great collection of ideas:
https://www.google.co.uk/url?sa=t&r...ircuits.html&usg=AOvVaw0eOw9Ues5E8nILXkLmYvNv

 

hi j,
This is the 2N3819 datasheet.
E

EDIT:
Check this link for equivalent.
https://english.electronica-pt.com/components-cross-reference?ref=2N3819

dear eric,

finally i order the 2N3819 JFET. but delivery time is a week. is that need to replace the LM324( ampifier( U2,U4,U6) and V-I (U1,U3) coverter)ic with standard one to improve the circuit because i found one website in my country who are ready to deliver some standard components... can you suggests me?

 

hi,
In post #32, you said you had the LM358 option, that is the OPA I have been using in the simulations, not the LM324
E

 

I think this jfet thing is a red herring its thermal stability is not that great. Use smarter current summing see AD CN-0295:

 

hi,
In post #32, you said you had the LM358 option, that is the OPA I have been using in the simulations, not the LM324
E

sorry eric... i used LM358 only
now i can have a option to use some standard.. is that really need to replace LM358 with other one or not?

 

hi rajit,
I do not know what types of OPA you can purchase in your area.?
Give me a short list list of OPA's that you can buy and I will try to select one from your list
E