Could you please suggest me some good current sensor module for my application?

Discussion in 'General Electronics Chat' started by musthafafarhan, Nov 18, 2015.

  1. musthafafarhan

    Thread Starter New Member

    Nov 18, 2015
    6
    0
    More information:

    I need to sense the current between the load and power supply. In this case. the load is a stepper motor which normally operates in 24V given from the power supply unit. My goal is to find the force of the motor, If I want to find the force, I need to know the torque value.

    In my project , I have no option to find the torque of the motor so I only way to find the current (different speed has different current value) so that I need to buy the current sensor module.

    please suggest me the right product which ill give the good accuracy and result. <<please also refer attached image for the general idea>>
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Best way to sense current is with a Hall Effect device. Just find one for the level of current you're expecting to measure. I use one to measure 40A for my trolling motor. You'll need something that measures much lower current.
     
  3. musthafafarhan

    Thread Starter New Member

    Nov 18, 2015
    6
    0
    Thank you. As I was focusing on shunt resistor based sensing module and I was also researched little bit about hall sensor based current sensing module. I wonder if you could let me know some difference in shunt resistor based and hall effect based. Moreover if you could let me know the model of the sensor you used, would more helpful for me because if it is good for my application I can take some time to study about that product.
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    I'll have to go back through my records. I purchased them years ago. More to follow...
     
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,907
    2,165
    http://www.allegromicro.com/en/Desi...nt-Trends-in-Hall-Effect-Current-Sensing.aspx
    http://www.intersil.com/content/dam/Intersil/whitepapers/amplifiers/current-sense-measurements.pdf

    Hall based sensors have very low path resistance (PCB devices) while offering total galvanic isolation in the kV range with a direct micro-controller interface. Hard to beat for size and performance today with a shunt-based design.

    If you need good accuracy and temperature stability then be sure to use a stable voltage source for the Hall-sensor and the ADC reference if you're converting an analog output from the sensor.
     
    Last edited: Nov 19, 2015
  6. musthafafarhan

    Thread Starter New Member

    Nov 18, 2015
    6
    0
    could you please give some list of sensor module (a complete circuit board). which means I dont need to connect any outside components rather input and output for the motors and power supply or oscilloscope. If I know some suggested product will be easy to pick one. because It is just a part of small application in my big project so I dont think it is worth to spend tons of time as I am already engaging with with other design related mechanical parts. Please help as not much experience in electronic design. Thank you again.
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
  8. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Wait a minute guys. A stepper motor is not like a normal motor. When you pulse a stepper motor, it moves a finite amount with each pulse and uses a finite amount of current with each pulse. Torque loading of the stepper motor has very little impact on the current draw. I think if you put a normal current sensor on a stepper you would read the same current regardless of the torque. I think monitoring duty factor would give you a better torque reading.


    Here is a link to a forum that talks about this issue.
    http://forums.parallax.com/discussion/118265/current-sensing-for-stepper-dc-motor-feedback
     
  9. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    I don't see how a stepper would get around the old conservation of energy principle.
     
  10. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    If you could average the current reading over a long period of time you would be right. With a stepper motor you do not have to measure the current because you know that each pulse represents the same amount of current. Whether the shaft is stalled or free wheeling the current does not change. You just need to measure how often those pulses occur. This is a lot easier and cheaper than measuring current.
     
  11. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    In other words...
    A resistor/capacitor averaging circuit on the drive signal to the stepper driver would give you as accurate torque measurement as if you used an expensive hall effect current sensor, and a resistor/capacitor averaging circuit. You do not need to measure the current because it will be the same for all pulses.
     
  12. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Oops, I made a mistake. You can not measure torque in a stepper motor. Since output torque does not reflect a change in coil current, you can not determine output torque by any voltage/current input measurements.
     
  13. musthafafarhan

    Thread Starter New Member

    Nov 18, 2015
    6
    0
    Actually, another idea is, we can sense the force by measuring the current. once we know the force we can easily find the torque. I am approaching current sensing method to primarily find the force. and then force * Distance will give the torque value
     
  14. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The current changes very little with torque. So, your current measurements will have no meaning. A stepper motor is not like a DC motor where current translates directly to torque. They are different devices and behave differently. One is a motor and the other is more like a relay. In a relay, the coil current is unaffected by the contact current. Do you get it??
     
  15. musthafafarhan

    Thread Starter New Member

    Nov 18, 2015
    6
    0
    I will go through the study regarding this and come back here. anyway, Thank you for your effort in supporting my discussion.
     
  16. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    I understand what Lestravled is saying, and he might have more experience with steppers than I do, but these motors are certainly subject to the same forces as any electro-magnetic machine. In order to do more work, more energy must be supplied to the machine. Although there are significant differences, basic mechanisms are a play. A set of coils are energized to set up a magnetic field which moves an armature. As the armature moves, back emf prevents the coil current from running away. More current means stronger magnetic field, which would would be necessary to overcome a stronger force, and thus do more work. A stronger resistive force on the armature means less back emf, thus more current draw.

    However, Les is correct when talking about the motor moving a small amount for each pulse. Once the motor has moved its 'step', back emf no longer exists in the coil, and the current is free to run away, due to low coil resistance. Thus, it is important to limit current. This give rise to a balance between maximum torque available, and a safe operating area for the motor.

    Here is a pretty good discussion: (click on 'Controlling The Motor')

    http://www.phidgets.com/docs/Stepper_Motor_and_Controller_Primer#Setting_the_Current_Limit
     
  17. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
    1,247
    If I understand Les's point, a stepper motor basically draws the same current no matter what the load. This is entirely consistent with conventional energy concepts if you view the motor as something that is extremely inefficient at low loads, a constant power device rather than a constant torque device. This is consistent with my own experience of steppers running at about the same temperature with and without loading.

    ak
     
  18. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Still, I see nothing about a the magnetic work done by a stepper motor that should make it any more inefficient at low loads than any other motor, with which in my experience, draws less power for lighter loads (some of which draws 7 times the current at locked rotor than during no load) However, after reviewing some, the difference observed with steppers might come from the fact that the motor remains energized after reaching it's 'position' and requires current limiting to prevent over heating while stopped, and with the magnetic poles aligned ( no more back EMF ) This would then require that the current be the same regardless of the load, within limits, assuming the current limiting is constant.

    Thus, I conceded the point to @Lestraveled. Current measurement probably won't provide anything useful.
     
  19. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    We both learned something.
     
  20. Techno Tronix

    Member

    Jan 10, 2015
    140
    10
    What about Spark Fun Hall-Effect Current Sensor Breakout - ACS712. The sensor gives precise current measurement for both AC and DC signals. Thick copper conductor and signal traces allows for survival of the device up to 5 times over current conditions.
     
Loading...