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#1
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Themocouple RF antenna current meters.
Came across a couple of those RF antenna current meters. Typical they
have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. |
#2
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Themocouple RF antenna current meters.
Well, they could be either a self-contained meter; one that one hooks up
directly, inline/series, with the RF current and the other is as you have described. If the meters are not of the sealed type, you can remove the movement from the shell and have a look. Try and see if there's a thermocouple mounted somewhere as an integral part of the unit. Meters, like on the TCS, BC-191/375, and the ART-13 for example, are self-contained. They generally all work the same, its just where the thermocouple is located. That's my observation on the subject..... terryS wrote: Came across a couple of those RF antenna current meters. Typical they have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. |
#3
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Themocouple RF antenna current meters.
The May 1969 issue of Popular Electronics has plans to make a 5 Amp. AC
Ammeter out of a BC-442 meter. It uses 300 ohm twin lead as a 0.1375 ohm shunt. They show 31" plus 1/2" for connections at each end. I have the proper meter but never acquired the thermocouple. K3HVG wrote: Well, they could be either a self-contained meter; one that one hooks up directly, inline/series, with the RF current and the other is as you have described. If the meters are not of the sealed type, you can remove the movement from the shell and have a look. Try and see if there's a thermocouple mounted somewhere as an integral part of the unit. Meters, like on the TCS, BC-191/375, and the ART-13 for example, are self-contained. They generally all work the same, its just where the thermocouple is located. That's my observation on the subject..... terryS wrote: Came across a couple of those RF antenna current meters. Typical they have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. |
#4
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Themocouple RF antenna current meters.
Richard Hall wrote:
The May 1969 issue of Popular Electronics has plans to make a 5 Amp. AC Ammeter out of a BC-442 meter. It uses 300 ohm twin lead as a 0.1375 ohm shunt. They show 31" plus 1/2" for connections at each end. I have the proper meter but never acquired the thermocouple. What type is the thermocouple? If it's a Type J or K, I probably have some junk box stuff. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#5
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Themocouple RF antenna current meters.
Richard Hall writes:
The May 1969 issue of Popular Electronics has plans to make a 5 Amp. AC Ammeter out of a BC-442 meter. It uses 300 ohm twin lead as a 0.1375 ohm shunt. They show 31" plus 1/2" for connections at each end. I have the proper meter but never acquired the thermocouple. K3HVG wrote: Well, they could be either a self-contained meter; one that one hooks up directly, inline/series, with the RF current and the other is as you have described. If the meters are not of the sealed type, you can remove the movement from the shell and have a look. Try and see if there's a thermocouple mounted somewhere as an integral part of the unit. Meters, like on the TCS, BC-191/375, and the ART-13 for example, are self-contained. They generally all work the same, its just where the thermocouple is located. That's my observation on the subject..... terryS wrote: Came across a couple of those RF antenna current meters. Typical they have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. It is the BC-442 antenna current meter. I built the meter from the article. Still use it. Fair Radio had the thermocouple units-- now out of stock, but it might be worth an email. Steve. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#6
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Themocouple RF antenna current meters.
You can easily determine if the meter is a remote reading meter or one with
a built in thermocouple. Put a digital ohmmeter on the meter leads. if the resistance is very low, then the thermocuple is built in. If the resistance reads tens of ohms or more, it is a simple dc meter that can be used for any purpose. I have found that many of the remote reading meters are not calibrated in actual amps, but are relative reading. Often the rf ammeters that are self contained contain a bakelite or formica back to give clearance to the rf. Colin K7FM |
#7
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Themocouple RF antenna current meters.
"COLIN LAMB" writes:
You can easily determine if the meter is a remote reading meter or one with a built in thermocouple. Put a digital ohmmeter on the meter leads. if the resistance is very low, then the thermocuple is built in. If the resistance reads tens of ohms or more, it is a simple dc meter that can be used for any purpose. I have found that many of the remote reading meters are not calibrated in actual amps, but are relative reading. Often the rf ammeters that are self contained contain a bakelite or formica back to give clearance to the rf. Colin K7FM http://www.fairradio.com/catalog.php...witem&item=551 -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#8
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Themocouple RF antenna current meters.
In article .com,
"terryS" wrote: Came across a couple of those RF antenna current meters. Typical they have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. The British ones (black bakelite cases) almost always have the thermocouple built into the meter. They will usually be marked "Thermocouple" or "For Radio Frequency Only" on the dial, and the resistance is usually shown as well. Be careful: the thermocouple is *VERY* delicate and will not stand up to overload - the nichrome wire melts and it's useless thereafter. (I've blown up an ex-Admiralty plug-in meter that was scaled 0-500mA but had "requires x20 shunt" pencilled very faintly on the back.) Chris. -- If it doesn't contravene the Criminal Justice Act (1988) it has no place in a kitchen. -- Peter Corlett in the scary devil monastery. |
#9
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Themocouple RF antenna current meters.
On Mar 4, 8:57 am, (Chris Suslowicz) wrote:
In article .com, "terryS" wrote: Came across a couple of those RF antenna current meters. Typical they have a scale up to three of five amps. One is US and other is UK war surplus. AIUI the meter movement is driven by a small DC current produced from the output of the thermocouple. The thermocouple being heated by the RF current. Looks like the meter itself is a one or five milliamp movement. Can anyone comment/advise? Thanks. The British ones (black bakelite cases) almost always have the thermocouple built into the meter. They will usually be marked "Thermocouple" or "For Radio Frequency Only" on the dial, and the resistance is usually shown as well. Be careful: the thermocouple is *VERY* delicate and will not stand up to overload - the nichrome wire melts and it's useless thereafter. (I've blown up an ex-Admiralty plug-in meter that was scaled 0-500mA but had "requires x20 shunt" pencilled very faintly on the back.) Chris. Thanks Chris and others. Part of what I was wondering is a seemingly 'dud' RF ammeter. The movement might be OK and could be, say, 1 or 5 milliamp etc. fsd. |
#10
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Themocouple RF antenna current meters.
In article .com,
"terryS" wrote: Thanks Chris and others. Part of what I was wondering is a seemingly 'dud' RF ammeter. The movement might be OK and could be, say, 1 or 5 milliamp etc. fsd. Ah, right. In that case: The ex-RAF meters (marked A (crown) M for Air Ministry) have the resistance wire soldered directly to the back of the terminals on the case. The thermocouple is then spotwelded to the middle of the resistance wire, and one lead goes to one side of the movement directly, the other goes via a "coil spring" of nichrome resistance wire (length cut to get the thermocouple calibration correct) to the other side of the movement. If it's open circuit across the terminals, then the resistance element has blown. The thermocouple and movement should still be perfectly OK. (I've considered trying to replace the resistance wire but calibrating it will be the difficult part.) Somewhere I have a box of dead meters.... I may be some time. Chris. -- Most uses of "spider" have noninsect meanings. -- Christine Malcom-Dept. |
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