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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Galvanometer
I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#2
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Galvanometer
In article ,
David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? With a standard alkaline cell and starting with a *very high* resistance (5 megohms, say), drop the resistance until you get a decent deflection. Then measure the resistance and the voltage, and do the math. Isaac |
#3
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Galvanometer
On 4/12/2009 8:08 PM isw spake thus:
In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? With a standard alkaline cell and starting with a *very high* resistance (5 megohms, say), drop the resistance until you get a decent deflection. Then measure the resistance and the voltage, and do the math. Figure it out for myself? What a concept! So, OK, I did as you suggested. Actually, the thing was a *lot* less sensitive than you warned; I ended up using 2 AA cells (2.95 volts according to 2 DMMs) through less than 10K to get a decent deflection from the meter. So here's my work, which you can check: The needle went left to 18. I = V (2.95) / R (7.45K) = 0.0004A (rounded) = 0.4mA Dividing this by 18 shows that each division on the meter is 0.02mA. So I hooked the thing up to one channel's mike input on my Sony D6 Walkman (see posts rehantom powering from this device above) through an appropriate load resistor, and the meter went to 15, which tells me that it was supplying 0.3mA. (Did the same thing even without any load resistor.) Not much power. (Even less than Eeyore had predicted this unit would be able to supply.) Can't use that to power my microphone as I'd hoped. Oh, well. -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#4
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Galvanometer
In article ,
David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? Most meter *movements* will only read directly small currents or voltages. To allow them to read higher values you use an appropriate resistor - in series to read a higher voltage than the FSD of the movement or in parallel to read a higher current. So the exact same movement can be supplied with a variety of scales for different applications - and may or may not include this resistor, which is called a shunt for current and multiplier for voltage. If it includes this resistor the scale is usually marked with the true units. 30-0-30 was common for the ammeter on older cars. -- *The average person falls asleep in seven minutes * Dave Plowman London SW To e-mail, change noise into sound. |
#5
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Galvanometer
On 4/13/2009 1:26 AM Dave Plowman (News) spake thus:
In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? Most meter *movements* will only read directly small currents or voltages. To allow them to read higher values you use an appropriate resistor - in series to read a higher voltage than the FSD of the movement or in parallel to read a higher current. Yes, I know all that. So the exact same movement can be supplied with a variety of scales for different applications - and may or may not include this resistor, which is called a shunt for current and multiplier for voltage. If it includes this resistor the scale is usually marked with the true units. No shunt resistor. See my post above: turns out each division is 0.02mA (0.6mA full scale). Meter is labeled "DC GALVANOMETER", by the way. I'm thinking it was a piece of lab equipment, or maybe for students to learn to use stuff like Wheatstone bridges, etc. 30-0-30 was common for the ammeter on older cars. How do you get from "galvanometer" to automobile ammeter??? Helpfulness of your post: 0.2 (dimensionless units). -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#6
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Galvanometer
In article ,
David Nebenzahl wrote: On 4/13/2009 1:26 AM Dave Plowman (News) spake thus: In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? Most meter *movements* will only read directly small currents or voltages. To allow them to read higher values you use an appropriate resistor - in series to read a higher voltage than the FSD of the movement or in parallel to read a higher current. Yes, I know all that. Then why the post? You have all the information to work it out for yourself. So the exact same movement can be supplied with a variety of scales for different applications - and may or may not include this resistor, which is called a shunt for current and multiplier for voltage. If it includes this resistor the scale is usually marked with the true units. No shunt resistor. See my post above: turns out each division is 0.02mA (0.6mA full scale). Meter is labeled "DC GALVANOMETER", by the way. I'm thinking it was a piece of lab equipment, or maybe for students to learn to use stuff like Wheatstone bridges, etc. Similar meters are - or were - on sale in most hobby electronics shops. 30-0-30 was common for the ammeter on older cars. How do you get from "galvanometer" to automobile ammeter??? FFS, a 'galvanometer' *is* an ammeter. Or is it yet another term you want to mean whatever you think it should? And 30-0-30 is exactly how older car ammeters were marked. No need for 'amps' as that's all it could be. And external ones for garage use (on cars not so fitted) were to be found. Helpfulness of your post: 0.2 (dimensionless units). You really are a charmer. -- *I want it all and I want it delivered Dave Plowman London SW To e-mail, change noise into sound. |
#7
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Galvanometer
In article t, msg wrote:
David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. Michael I also though of a sensitive current or sensitive votmeter. I actually though of a static vane type, but there is also the iron vane galvanometer. The key was the center scale 0. greg |
#8
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Galvanometer
David Nebenzahl wrote:
I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. Michael |
#9
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Galvanometer
On 4/13/2009 9:39 AM msg spake thus:
David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. Well, this one is definitely marked as such (at the factory), and was made by what was at the time one of the largest manufacturers of meters in the U.S., Weston Electrical Instrument Corp. Make of that what you will. -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#10
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Galvanometer
In article , David Nebenzahl wrote:
On 4/13/2009 9:39 AM msg spake thus: David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. Well, this one is definitely marked as such (at the factory), and was made by what was at the time one of the largest manufacturers of meters in the U.S., Weston Electrical Instrument Corp. Make of that what you will. Here is one I have.... http://zekfrivolous.com/misc/meter.JPG |
#11
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Galvanometer
On 4/13/2009 11:19 AM GregS spake thus:
In article , David Nebenzahl wrote: On 4/13/2009 9:39 AM msg spake thus: David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. Well, this one is definitely marked as such (at the factory), and was made by what was at the time one of the largest manufacturers of meters in the U.S., Weston Electrical Instrument Corp. Make of that what you will. Here is one I have.... http://zekfrivolous.com/misc/meter.JPG Except ... it's not labeled as a galvanometer. Nice piece, though; much nicer looking than my utilitarian black crackle job. -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#12
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Galvanometer
On Sun, 12 Apr 2009 20:08:37 -0700, isw put finger
to keyboard and composed: In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? With a standard alkaline cell and starting with a *very high* resistance (5 megohms, say), drop the resistance until you get a decent deflection. Then measure the resistance and the voltage, and do the math. Isaac A quicker way to do it might be to use two DMMs. Set the first to measure resistance and the second to measure current. Start with the highest resistance scale. DMM1 will supply a test current to the other two meters. DMM1 (ohms) DMM2 (amps) Weston Galvanometer -- I -- I o---------o-- A --o---------o-- M --o--| | | current | source | | | o--------------------------------------| I -- My DMM outputs the following test currents: diode - 0.93mA 200R - 167uA 2K - 133uA 20K - 42uA 200K - 5uA 2M - 0.5uA When testing on the diode range, the OP could set DMM2 for the highest burden, ie the 2M scale. In that way the voltage to the galvanometer would be reduced by 200mV (?). Alternatively he could insert a series resistor or potentiometer. If only one DMM is available, then replace DMM1 with a battery and resistor and use your DMM to measure the current, otherwise you will need to account for the burden of the galvanometer when doing your Ohm's Law calculations. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#13
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Galvanometer
"Franc Zabkar" wrote in message ... On Sun, 12 Apr 2009 20:08:37 -0700, isw put finger to keyboard and composed: In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? With a standard alkaline cell and starting with a *very high* resistance (5 megohms, say), drop the resistance until you get a decent deflection. Then measure the resistance and the voltage, and do the math. Isaac A quicker way to do it might be to use two DMMs. Set the first to measure resistance and the second to measure current. Start with the highest resistance scale. DMM1 will supply a test current to the other two meters. DMM1 (ohms) DMM2 (amps) Weston Galvanometer -- I -- I o---------o-- A --o---------o-- M --o--| | | current | source | | | o--------------------------------------| I -- My DMM outputs the following test currents: diode - 0.93mA 200R - 167uA 2K - 133uA 20K - 42uA 200K - 5uA 2M - 0.5uA When testing on the diode range, the OP could set DMM2 for the highest burden, ie the 2M scale. In that way the voltage to the galvanometer would be reduced by 200mV (?). Alternatively he could insert a series resistor or potentiometer. If only one DMM is available, then replace DMM1 with a battery and resistor and use your DMM to measure the current, otherwise you will need to account for the burden of the galvanometer when doing your Ohm's Law calculations. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. Every galvanometer I've seen in the past 60 years read in microamps |
#14
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Galvanometer
"David Nebenzahl" wrote in message .com... On 4/13/2009 9:39 AM msg spake thus: David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. That instrument was called a "ballistic galvanometer" and was intended to measure very small currents for a very short duration, the mirror would deflect with the current and return very slowly so you could grab a reading on the current. Well, this one is definitely marked as such (at the factory), and was made by what was at the time one of the largest manufacturers of meters in the U.S., Weston Electrical Instrument Corp. Make of that what you will. -- Save the Planet Kill Yourself - motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/) |
#15
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Galvanometer
On Mon, 13 Apr 2009 21:54:51 GMT, "att" put finger to
keyboard and composed: Every galvanometer I've seen in the past 60 years read in microamps The OP's measurements suggest that the meter's fsd is +/- 600uA, not +/- 30uA. Therefore it probably has a current shunt. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#16
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Galvanometer
In article ,
David Nebenzahl wrote: On 4/12/2009 8:08 PM isw spake thus: In article , David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? With a standard alkaline cell and starting with a *very high* resistance (5 megohms, say), drop the resistance until you get a decent deflection. Then measure the resistance and the voltage, and do the math. Figure it out for myself? What a concept! So, OK, I did as you suggested. Actually, the thing was a *lot* less sensitive than you warned; I ended up using 2 AA cells (2.95 volts according to 2 DMMs) through less than 10K to get a decent deflection from the meter. So here's my work, which you can check: The needle went left to 18. I = V (2.95) / R (7.45K) = 0.0004A (rounded) = 0.4mA Dividing this by 18 shows that each division on the meter is 0.02mA. So I hooked the thing up to one channel's mike input on my Sony D6 Walkman (see posts rehantom powering from this device above) through an appropriate load resistor, and the meter went to 15, which tells me that it was supplying 0.3mA. (Did the same thing even without any load resistor.) Not much power. (Even less than Eeyore had predicted this unit would be able to supply.) Can't use that to power my microphone as I'd hoped. Oh, well. That sort of input is intended to power an electret condenser mic (with possibly a FET follower). It basically needs a polarizing voltage at nearly zero current. Isaac |
#17
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Galvanometer
In article
, "att" wrote: "David Nebenzahl" wrote in message .com... On 4/13/2009 9:39 AM msg spake thus: David Nebenzahl wrote: I have an old galvanometer (nice Weston in a slant-front black crackle case). Its scale reads 30-0-30. What units are these? Or are they just relative values for comparison? When you said 'galvanometer', I immediately expected you to be talking about a 'mirror galvanometer': a large sensitive laboratory instrument rather than an ordinary moving coil meter, which of course is also a 'galvanometer' but is not commonly (at least in the US) labeled as such. That instrument was called a "ballistic galvanometer" and was intended to measure very small currents for a very short duration, the mirror would deflect with the current and return very slowly so you could grab a reading on the current. A "ballistic galvanometer" is rather a different beast from a normal galvo -- for one thing, the suspension has essentially no restoring force (and that is why the return is so slow; not just to make it easier to read). A normal galvo deflects to the angle where the *continuous* force from the current is matched by the restoring spring force of the suspension. "Ballistic" refers to the fact that the galvo is intended to accept a brief pulse of current and then respond "ballistically" -- integrating the pulse -- by producing a deflection proportional, essentially, to the total number of electrons that just flowed through its coil. In fact, the pulse should be short enough so that it is completely over before the deflection begins. In general, just about *any* continuous current you put through a ballistic galvo will cause it to deflect all the way to the stops (because the restoring force is so small). Isaac |
#18
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Ballisitc Galvanometer
On Tue, 14 Apr 2009 22:11:42 -0700, isw wrote
about ballistic galvanometers. Thanks for the refresher! I'd forgotten about ballistic galvo's. Your description of minimal restoring force reminds me of the very distinctive traditional Megger meter movements; their hairsprings (three of them) were tweaked for no net restoring force. Btw, "galvanometer" is a term from more than a century ago; iirc, it refers to Luigi Galvani, of voltaic pile and jumping frog's legs, etc. Regards, nb |
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