Hello ja7me
Let us see things in parts:
Is the LM317 configured as a current regulator?
NO as a voltage regulator but current regulator.
If so, note that the output current will pass through the potentiometer setting.
The pot supports that current?
Note that in the loop formed by: the current regulator and the resistor under test (RUT) must have some very good connections.
Otherwise vary the millivoltmeter reading. in other words: the reading fluctuates.
Because the readings are in the range of low voltage, fluctuations in the reading may also occur by ambient electromagnetic noise.
The poor quality of the RUT can produce also instability in the readings.
You already looked at the data sheets of the LM317 ?
Probably it is exceeding a parameter and is therefore not regulate the current as expected.
As per you writings I can see that your current regulator is NOT working fine.
A current regulator must maintain its output current no matter how you change the RUT.
Of course there is a range for the maximum value for this RUT.
This depends on how much voltage, the current regulator has, to apply the current against the RUT.
And also the electrical characteristics of the LM317.
your writings:
my writings:
LOW OHM METER EXPERIMENT:
Parts:
Regulator = LM317
Ra = Adjustment resistor
Rload = Resistor to be measured
Vs = 6V
When:
Ra = 120Ohm
Rload = 2.2Ohm
Vload = 0.024
Panel meter reads 1.87
V/R= I, 0.024 / 2.2 = 10.91 mAmp.
Vin Vout, 6 0.024 = 5.976 Volts.
When:
Ra = 120Ohm
Rload = 4.4Ohm
Vload = 0.047
Panel meter reads 4.10
V/R=I, 0.047 / 4.4 = 10.68 mAmp.
Vin Vout, 6 0.047 = 5.53 Volts.
Also I tried a variable resistor for Ra, so that I could adjust the the panel meter display to read the correct resistance:
When:
Ra = Variable resistor
Rload = 2.2Ohm
Vload = 0.028V
Panel meter reads 2.20
V/R=I, 0.028 / 2.2 = 12.72 mAmp.
Vin Vout, 6 0.028 = 5.972 Volts.
When:
Ra = Variable resistor
Rload = 4.4Ohm
Vload = 0.054V
Panel meter reads 4.80
V/R=I, 0.054 / 4.4 = 12.27 mAmp.
Vin Vout, 6 0.054 = 5.946 Volts.
When:
Ra = Variable resistor
Rload = 6.8Ohm
Vload = 0.082V
Panel meter reads 7.53
V/R=I, 0.082 / 6.8 = 12.058 mAmp.
Vin Vout, 6 0.082 = 5.918 Volts.
regards
at your service
Let us see things in parts:
Is the LM317 configured as a current regulator?
NO as a voltage regulator but current regulator.
If so, note that the output current will pass through the potentiometer setting.
The pot supports that current?
Note that in the loop formed by: the current regulator and the resistor under test (RUT) must have some very good connections.
Otherwise vary the millivoltmeter reading. in other words: the reading fluctuates.
Because the readings are in the range of low voltage, fluctuations in the reading may also occur by ambient electromagnetic noise.
The poor quality of the RUT can produce also instability in the readings.
You already looked at the data sheets of the LM317 ?
Probably it is exceeding a parameter and is therefore not regulate the current as expected.
As per you writings I can see that your current regulator is NOT working fine.
A current regulator must maintain its output current no matter how you change the RUT.
Of course there is a range for the maximum value for this RUT.
This depends on how much voltage, the current regulator has, to apply the current against the RUT.
And also the electrical characteristics of the LM317.
your writings:
my writings:
LOW OHM METER EXPERIMENT:
Parts:
Regulator = LM317
Ra = Adjustment resistor
Rload = Resistor to be measured
Vs = 6V
When:
Ra = 120Ohm
Rload = 2.2Ohm
Vload = 0.024
Panel meter reads 1.87
V/R= I, 0.024 / 2.2 = 10.91 mAmp.
Vin Vout, 6 0.024 = 5.976 Volts.
When:
Ra = 120Ohm
Rload = 4.4Ohm
Vload = 0.047
Panel meter reads 4.10
V/R=I, 0.047 / 4.4 = 10.68 mAmp.
Vin Vout, 6 0.047 = 5.53 Volts.
Also I tried a variable resistor for Ra, so that I could adjust the the panel meter display to read the correct resistance:
When:
Ra = Variable resistor
Rload = 2.2Ohm
Vload = 0.028V
Panel meter reads 2.20
V/R=I, 0.028 / 2.2 = 12.72 mAmp.
Vin Vout, 6 0.028 = 5.972 Volts.
When:
Ra = Variable resistor
Rload = 4.4Ohm
Vload = 0.054V
Panel meter reads 4.80
V/R=I, 0.054 / 4.4 = 12.27 mAmp.
Vin Vout, 6 0.054 = 5.946 Volts.
When:
Ra = Variable resistor
Rload = 6.8Ohm
Vload = 0.082V
Panel meter reads 7.53
V/R=I, 0.082 / 6.8 = 12.058 mAmp.
Vin Vout, 6 0.082 = 5.918 Volts.
regards
at your service
Attachments
-
149.8 KB Views: 15
-
51.6 KB Views: 10