Im trying to get the attached Howland current source to work but Im not getting the right results. For Vin = 550mV and R = 130 I get roughly -4mA which is correct but for Vin = 2.7 and R = 130 I get -6mA when I should get roughly 20mA. Can anyone suggest why?

 

How do you measures the current? I real circuit?

 

from the pic, I have a probe where the load is on my simulation and have ran a transient analysis.

 

Well you need to post actual schematic of the circuit that you use in the simulation.
What is the value of a load resistor ?

 

the circuit is too big to post, but I have a rectified AC voltage that has been smoothed by a LPF at the input to the current source. not sure what a load resistor is?

 

Show full diagram of a current source.
What type op amp you have used? What supply voltage was? And which component is connect to your current source output. What is the value of this component?

 

I have simulated the current source with no load just a multimeter connected to the node between the bottom 2 resistors. I have just used a dc source, but when I actually make it on a breadboard with a dc power supply of +10V and -10V and using another DC power supply as the input signal I get nothing out of the output at pin 3.

 

I have used 4 150 ohm resistors and an input of 7V

 

You should be aware that in real life most op amps will not work properly with output current larger than >20mA. Also the input voltage 7V is too high for op amp supplied from a +/-10V power supply.

 

the max voltage for what Im doing is about 2.5V, What did you mean by the component connected to the output?