Addressing Electromagnetic Interference with Phidgets - Revision history

Burley: /* Grounding Problems */

2014-05-06T14:27:14Z

Grounding Problems

← Older revision		Revision as of 14:27, 6 May 2014
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	USB is not reliable if the voltage difference between either end of a USB cable is greater than 125mV. This is usually not a problem because the only current travelling on the USB cable should be less than 500mA (USB Maximum), and the cable resistance is designed to produce less than 125mV at 500mA current.		USB is not reliable if the voltage difference between either end of a USB cable is greater than 125mV. This is usually not a problem because the only current travelling on the USB cable should be less than 500mA (USB Maximum), and the cable resistance is designed to produce less than 125mV at 500mA current.

	It’s possible to for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.		It’s possible for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.

	[[File:Grounding Issue.jpg\|800px\|link=]]		[[File:Grounding Issue.jpg\|800px\|link=]]

Mparadis: /* Recommended Approach to EMI Problems */

2012-08-10T19:27:29Z

Mparadis at 19:15, 10 August 2012

2012-08-10T19:15:39Z

← Older revision		Revision as of 19:15, 10 August 2012
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			[[Category:General Documentation]]
	*Phidgets are sensitive to electromagnetic interference (EMI) due to their extreme flexibility.		*Phidgets are sensitive to electromagnetic interference (EMI) due to their extreme flexibility.
	*Phidgets are used every day to build reliable systems, but it’s very easy to build an unreliable system.		*Phidgets are used every day to build reliable systems, but it’s very easy to build an unreliable system.

Mparadis: /* Ferrite Beads */

2012-08-10T16:13:03Z

Ferrite Beads

← Older revision		Revision as of 16:13, 10 August 2012
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	==Ferrite Beads==		==Ferrite Beads==
			[[File:USBwithFerriteBead.jpg\|300px\|thumb\|link=\|A USB cable looped twice through a large ferrite bead.]]

	Ferrite beads are miracle devices for reducing high frequency problems. If clamped on a cable they will block most forms of unwanted energy. It is best to secure the ferrite bead near the end of the cable, as opposed to in the middle, to ensure the least amount of noise is affecting the cable at that end. We recommend installing a ferrite bead on USB cables close to the PC. Adding ferrite beads to long input wires close to where they attach to Phidgets will also be beneficial.		Ferrite beads are miracle devices for reducing high frequency problems. If clamped on a cable they will block most forms of unwanted energy. It is best to secure the ferrite bead near the end of the cable, as opposed to in the middle, to ensure the least amount of noise is affecting the cable at that end. We recommend installing a ferrite bead on USB cables close to the PC. Adding ferrite beads to long input wires close to where they attach to Phidgets will also be beneficial.

	~~[[File:USBwithFerriteBead~~.~~jpg\|400px\|thumb\|link=\|A~~ USB cable ~~looped twice through a large ferrite bead~~.]]		Our experimentation indicates that an extra loop through the ferrite bead is very helpful. Additional loops will often degrade protection. We suggest the ferrite bead shown above, as it is large enough to accommodate an extra loop of a USB cable, and can be easily snapped on or taken off. Digikey Part Number: 28A2736-0A2

	Our experimentation indicates that an extra loop through the ferrite bead is very helpful. Additional loops will often degrade protection. We suggest the ferrite bead shown above, as it is large enough to accommodate an extra loop of a USB cable, and can be easily snapped on or taken off. Digikey Part Number: 28A2736-0A2		<br clear=all>

	==Testing==		==Testing==

Mparadis: /* Ferrite Beads */

2012-08-10T16:12:26Z

Ferrite Beads

← Older revision		Revision as of 16:12, 10 August 2012
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	Ferrite beads are miracle devices for reducing high frequency problems. If clamped on a cable they will block most forms of unwanted energy. It is best to secure the ferrite bead near the end of the cable, as opposed to in the middle, to ensure the least amount of noise is affecting the cable at that end. We recommend installing a ferrite bead on USB cables close to the PC. Adding ferrite beads to long input wires close to where they attach to Phidgets will also be beneficial.		Ferrite beads are miracle devices for reducing high frequency problems. If clamped on a cable they will block most forms of unwanted energy. It is best to secure the ferrite bead near the end of the cable, as opposed to in the middle, to ensure the least amount of noise is affecting the cable at that end. We recommend installing a ferrite bead on USB cables close to the PC. Adding ferrite beads to long input wires close to where they attach to Phidgets will also be beneficial.

	[[File:~~placeholder~~.jpg\|~~center~~\|link=]]		[[File:USBwithFerriteBead.jpg\|400px\|thumb\|link=\|A USB cable looped twice through a large ferrite bead.]]

	Our experimentation indicates that an extra loop through the ferrite bead is very helpful. Additional loops will often degrade protection. We suggest the ferrite bead shown above, as it is large enough to accommodate an extra loop of a USB cable, and can be easily snapped on or taken off. Digikey Part Number: 28A2736-0A2		Our experimentation indicates that an extra loop through the ferrite bead is very helpful. Additional loops will often degrade protection. We suggest the ferrite bead shown above, as it is large enough to accommodate an extra loop of a USB cable, and can be easily snapped on or taken off. Digikey Part Number: 28A2736-0A2

Mparadis: /* Far Field Emissions */

2012-08-10T16:10:33Z

Far Field Emissions

← Older revision		Revision as of 16:10, 10 August 2012
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	\|		\|
	*Motors, especially DC motors.		*Motors, especially DC motors.
	*Motor emissions can be drastically reduced by putting a small capacitor (<1000 pF) across the motor terminal.		*Motor emissions can be drastically reduced by<br> putting a small capacitor (<1000 pF) across the motor terminal.
	\|		\|
	[[File:~~placeholder~~.jpg\|link=]]		[[File:MotorEmission.jpg\|link=\|400px\|Reducing Emissions caused by motors.]]
	\|}		\|}

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	\|		\|
	*For DC applications, a flyback diode will catch it.		*For DC applications, a flyback diode will catch it.
	\|[[File:~~placeholder~~.jpg\|link=]]		\|[[File:FlybackDiode.jpg\|link=\|300px\|Using a Flyback Diode.]]
	\|-		\|-
	\|		\|
	*For AC applications, use a bi-directional transient voltage suppression diode (transorb)		*For AC applications, use a bi-directional transient voltage suppression diode (transorb)
	\|[[File:~~placeholder~~.jpg\|link=]]		\|[[File:TVSDiode.jpg\|link=\|400px\|Using a Bi-directional TVS Diode.]]
	\|}		\|}

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	*Reduce the area by twisting the wires together that lead to the load.		*Reduce the area by twisting the wires together that lead to the load.

	[[File: ~~placeholder~~.jpg~~\|center~~\|link=]]		[[File:DealingWithAntennas.jpg\|link=]]

	==Near Field Emissions==		==Near Field Emissions==

Mparadis: /* Grounding Problems */

2012-08-10T15:30:35Z

Grounding Problems

← Older revision		Revision as of 15:30, 10 August 2012
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	It’s possible to for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.		It’s possible to for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.

	[[File: ~~placeholder~~.jpg\|link=~~\|center~~]]		[[File:Grounding Issue.jpg\|800px\|link=]]

	Grounding issues will manifest themselves as stability problems when using anything that consumes a lot of power, such as motors. The easiest solution is to use different power supplies for each Phidget in the system. This ensures that the current used by a Phidget (for example, the 1061 PhidgetAdvancedServo) and what it’s powering is kept within it’s domain – it recirculates between the power supply, the Phidget, and what is being powered. No extra current flows on the USB cable.		Grounding issues will manifest themselves as stability problems when using anything that consumes a lot of power, such as motors. The easiest solution is to use different power supplies for each Phidget in the system. This ensures that the current used by a Phidget (for example, the 1061 PhidgetAdvancedServo) and what it’s powering is kept within it’s domain – it recirculates between the power supply, the Phidget, and what is being powered. No extra current flows on the USB cable.

Burley: /* Grounding Problems */

2012-08-08T18:37:51Z

Grounding Problems

← Older revision		Revision as of 18:37, 8 August 2012
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	It’s possible to for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.		It’s possible to for the USB Cable to be carrying more than 500mA ground current if current is finding an alternative path back to it’s source. This can happen easily if you are using nonisolated power supplies, or using a single power supply to power multiple Phidgets.

	[[File: placeholder.jpg]]		[[File: placeholder.jpg\|link=\|center]]

	Grounding issues will manifest themselves as stability problems when using anything that consumes a lot of power, such as motors. The easiest solution is to use different power supplies for each Phidget in the system. This ensures that the current used by a Phidget (for example, the 1061 PhidgetAdvancedServo) and what it’s powering is kept within it’s domain – it recirculates between the power supply, the Phidget, and what is being powered. No extra current flows on the USB cable.		Grounding issues will manifest themselves as stability problems when using anything that consumes a lot of power, such as motors. The easiest solution is to use different power supplies for each Phidget in the system. This ensures that the current used by a Phidget (for example, the 1061 PhidgetAdvancedServo) and what it’s powering is kept within it’s domain – it recirculates between the power supply, the Phidget, and what is being powered. No extra current flows on the USB cable.

Burley: /* Some examples of Far Field emission sources */

2012-08-08T18:37:41Z

Some examples of Far Field emission sources

← Older revision		Revision as of 18:37, 8 August 2012
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	*Motor emissions can be drastically reduced by putting a small capacitor (<1000 pF) across the motor terminal.		*Motor emissions can be drastically reduced by putting a small capacitor (<1000 pF) across the motor terminal.
	\|		\|
	[[File:placeholder.jpg]]		[[File:placeholder.jpg\|link=]]
	\|}		\|}

Burley: /* Relays switching solenoids, motors with high current loads */

2012-08-08T18:37:36Z

Relays switching solenoids, motors with high current loads

← Older revision		Revision as of 18:37, 8 August 2012
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	\|		\|
	*For DC applications, a flyback diode will catch it.		*For DC applications, a flyback diode will catch it.
	\|[[File:placeholder.jpg]]		\|[[File:placeholder.jpg\|link=]]
	\|-		\|-
	\|		\|
	*For AC applications, use a bi-directional transient voltage suppression diode (transorb)		*For AC applications, use a bi-directional transient voltage suppression diode (transorb)
	\|[[File:placeholder.jpg]]		\|[[File:placeholder.jpg\|link=]]
	\|}		\|}

← Older revision		Revision as of 19:27, 10 August 2012
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	#Reduce emissions. Any sources of sparks or surges of current / voltage are suspect.		#Reduce emissions. Any sources of sparks or surges of current / voltage are suspect.
	#Reduce vulnerability. Sensitive circuitry should be kept short. USB cables, sensor cables and digital inputs are all antennas that receive emissions.		#Reduce vulnerability. Sensitive circuitry should be kept short. USB cables, sensor cables and digital inputs are all antennas that receive emissions.
	#Add another layer of protection after the system is stable. When your system is stable under your worst-case conditions, add ferrite beads to the USB cables, and possibly to the long sensor cables and digital inputs where they connect to the Phidgets.		#Add another layer of protection after the system is stable. When your system is stable under your worst-case conditions, add ferrite beads to the USB cables, and possibly to the long sensor cables and digital inputs where they connect to the Phidgets. For more information, see the [[Effects of Long Wires]] page.

	==Grounding Problems==		==Grounding Problems==