SteveOak
Gold $$ Contributor
TL;DR, get a battery.
This is not a white paper for a technical audience. The technical bits I include are to give a sense of the question and not to cover all possibilities and because sometimes I just can’t help myself. LOL I hope to keep it on a level that a non-technical person can appreciate the scope of the problems without being lost in technical mumbo jumbo but well enough to select a suitable solution for their application.
What will not be covered; physical environmental conditions that can affect the accuracy and/or performance of electronic scales such as temperature, vibration, air movement and the internal compensation electronics/algorithms for the load cell, all of which matter.
As far as my background, EMC is my day job. I am a Senior member of the IEEE EMC Society and a voting member of the SC-135 committee of the RTCA which is responsible for maintaining and updating DO-160, the FAA accepted document for qualifying electronic equipment with respect to electromagnetic interference and lightning to be permitted on passenger aircraft. I also do the military EMC stuff, MIL-STD 461 and 464 and system level certification for civil aircraft using ARP 5583.
The load cells used in electronic scales are cool little devices. They are very sensitive to displacement and able to detect a tiny amount of movement and convert it to electrical energy. They are also superb RF/Electromagnetic effects detectors.
There are three mechanisms by which electronic scales we would use for measuring powder can be influenced by electromagnetic interference, EMI for short.
1. Radiated, Electromagnetic energy propagated through the atmosphere which transfers into the electronics of the scale.
Some examples are intentional sources such as RF transmitted from your cell phone like 4G or 5G RF, WiFi, or Bluetooth.
Unintentional sources, secondary radiation from the chips in your phone or laptop and other electronic devices in your home or workshop.
2. Conducted, RF which has entered the power input wires to the scale or wall wart.
3. Input Power issues such as glitches, surges, sags, pops, momentary interrupts and noise generated by a switching power supply which is propagated through to the scale
Although technically not EMI, improper input power can affect the performance of the scale and is one type of tests we do for civil and military aircraft.
How to protect from type 1;
• Shielded cables for power and interconnect/communication
• wire overbraid made from tinned copper can be used to shield the cables
• the case, somewhere you can get to the frame of the scale
• the powder hopper, even if it is glass, it is better than dryer sheets
• this will also help some with static, you should also ground yourself with a wrist strap
How to protect from type 2
You really can’t do much of anything about it once it has gotten on the power and communication lines. Better to use shielded cables or overbraid to keep it from getting on the cables. If you get lucky and select a ferrite which is effective at the frequency(ies) where you were having an issue it might help but it is a shot in the dark at best.
A word about ferrites. Saying “I put a ferrite on the power cable” is like saying “I put some powder in the case” without saying what powder or how much or what case. Potentially less dangerous but no more meaningful. There are many different chemical compositions of ferrites, known as “types”, used for RFI mitigation. The composition, size and shape will cause the ferrite to affect different frequencies of RF from kilohertz to megahertz to gigahertz to differing amounts. They work by presenting an increased impedance to RF. To make them work optimally you need to provide an alternative path for the interference to travel so just plopping one on is only half the job and may not even be that much.
How to protect from type 3
Some may do nothing or have no benefit
Some of the better ones might help or even be pretty good.
Some may actually make things worse
See above
This is the best answer and one of the least expensive or at least greatest cost vs benefit. It will source clean, stable power, no junk from the utility company, no switching noise. A battery will sink RF. Set it up with a ‘y’ cable and a charger and keep it charged. Then you can, and should, DISCONNECT THE CHARGER FROM THE WALL when using the scale. Switching power supplies, especially the cheap ones in wall warts, generate a lot of interference, even when unloaded.
I recommend you not have a cell phone anywhere near your bench. Likewise, no Bluetooth devices. Some systems use a cell phone or laptop as a controller and/or display. Your choice.
Using a battery;
If you have chosen to use a battery be sure to size it adequately. Figure out what you need to run whatever you are running and for how long you run it at one sitting, then add 50%.
As you use energy from a battery the voltage will slowly decrease. This is not a big problem as your precision scale will have internal circuitry to convert the input voltage, let’s assume 12 VDC, down to the voltage or voltages used by the components/devices of the scale. It will not use 12 VDC for anything, you just don’t design electronics at this level that way. Probably the highest voltage it will use internally is 5 VDC. It will have voltage regulators to step the 12 VDC down to 5 VDC and/or whatever it uses. Drop of a volt or two is not likely to hurt anything. Since the intent of this exercise is to provide clean and proper power to your scale to ensure the most accurate and repeatable measurements, don’t cheap out here.
Charge the battery every time you use it!
If you are power other pieces of equipment, trickler or whatever, get a battery with larger capacity. Some of the LiPo batteries have considerable capacity in a very small case. But….the newer, high tech batteries may have internal electronic devices for charge management which may be a source of interference. They will probably have certification marks, CE, FCC, UL, but they may have only been tested to the safety requirements and not EMC, or, they may just put the label on it and never tested anything. I have seen that. A conventional battery without smarts, may be the best choice.
This is not a white paper for a technical audience. The technical bits I include are to give a sense of the question and not to cover all possibilities and because sometimes I just can’t help myself. LOL I hope to keep it on a level that a non-technical person can appreciate the scope of the problems without being lost in technical mumbo jumbo but well enough to select a suitable solution for their application.
What will not be covered; physical environmental conditions that can affect the accuracy and/or performance of electronic scales such as temperature, vibration, air movement and the internal compensation electronics/algorithms for the load cell, all of which matter.
As far as my background, EMC is my day job. I am a Senior member of the IEEE EMC Society and a voting member of the SC-135 committee of the RTCA which is responsible for maintaining and updating DO-160, the FAA accepted document for qualifying electronic equipment with respect to electromagnetic interference and lightning to be permitted on passenger aircraft. I also do the military EMC stuff, MIL-STD 461 and 464 and system level certification for civil aircraft using ARP 5583.
The load cells used in electronic scales are cool little devices. They are very sensitive to displacement and able to detect a tiny amount of movement and convert it to electrical energy. They are also superb RF/Electromagnetic effects detectors.
There are three mechanisms by which electronic scales we would use for measuring powder can be influenced by electromagnetic interference, EMI for short.
1. Radiated, Electromagnetic energy propagated through the atmosphere which transfers into the electronics of the scale.
Some examples are intentional sources such as RF transmitted from your cell phone like 4G or 5G RF, WiFi, or Bluetooth.
Unintentional sources, secondary radiation from the chips in your phone or laptop and other electronic devices in your home or workshop.
2. Conducted, RF which has entered the power input wires to the scale or wall wart.
3. Input Power issues such as glitches, surges, sags, pops, momentary interrupts and noise generated by a switching power supply which is propagated through to the scale
Although technically not EMI, improper input power can affect the performance of the scale and is one type of tests we do for civil and military aircraft.
How to protect from type 1;
- Shielding
• Shielded cables for power and interconnect/communication
• wire overbraid made from tinned copper can be used to shield the cables
- Grounding
• the case, somewhere you can get to the frame of the scale
• the powder hopper, even if it is glass, it is better than dryer sheets
• this will also help some with static, you should also ground yourself with a wrist strap
How to protect from type 2
You really can’t do much of anything about it once it has gotten on the power and communication lines. Better to use shielded cables or overbraid to keep it from getting on the cables. If you get lucky and select a ferrite which is effective at the frequency(ies) where you were having an issue it might help but it is a shot in the dark at best.
A word about ferrites. Saying “I put a ferrite on the power cable” is like saying “I put some powder in the case” without saying what powder or how much or what case. Potentially less dangerous but no more meaningful. There are many different chemical compositions of ferrites, known as “types”, used for RFI mitigation. The composition, size and shape will cause the ferrite to affect different frequencies of RF from kilohertz to megahertz to gigahertz to differing amounts. They work by presenting an increased impedance to RF. To make them work optimally you need to provide an alternative path for the interference to travel so just plopping one on is only half the job and may not even be that much.
How to protect from type 3
- Power conditioners
Some may do nothing or have no benefit
Some of the better ones might help or even be pretty good.
Some may actually make things worse
- Ferrites
See above
- Battery
This is the best answer and one of the least expensive or at least greatest cost vs benefit. It will source clean, stable power, no junk from the utility company, no switching noise. A battery will sink RF. Set it up with a ‘y’ cable and a charger and keep it charged. Then you can, and should, DISCONNECT THE CHARGER FROM THE WALL when using the scale. Switching power supplies, especially the cheap ones in wall warts, generate a lot of interference, even when unloaded.
I recommend you not have a cell phone anywhere near your bench. Likewise, no Bluetooth devices. Some systems use a cell phone or laptop as a controller and/or display. Your choice.
Using a battery;
If you have chosen to use a battery be sure to size it adequately. Figure out what you need to run whatever you are running and for how long you run it at one sitting, then add 50%.
As you use energy from a battery the voltage will slowly decrease. This is not a big problem as your precision scale will have internal circuitry to convert the input voltage, let’s assume 12 VDC, down to the voltage or voltages used by the components/devices of the scale. It will not use 12 VDC for anything, you just don’t design electronics at this level that way. Probably the highest voltage it will use internally is 5 VDC. It will have voltage regulators to step the 12 VDC down to 5 VDC and/or whatever it uses. Drop of a volt or two is not likely to hurt anything. Since the intent of this exercise is to provide clean and proper power to your scale to ensure the most accurate and repeatable measurements, don’t cheap out here.
Charge the battery every time you use it!
If you are power other pieces of equipment, trickler or whatever, get a battery with larger capacity. Some of the LiPo batteries have considerable capacity in a very small case. But….the newer, high tech batteries may have internal electronic devices for charge management which may be a source of interference. They will probably have certification marks, CE, FCC, UL, but they may have only been tested to the safety requirements and not EMC, or, they may just put the label on it and never tested anything. I have seen that. A conventional battery without smarts, may be the best choice.
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