At one my work stations where I put together small prototypes I finally discovered why the desoldering vacuums wand needs to be set higher in temp. I just wrote it off as a defective sensing circuit in the station because I tried another wand on it. However, the other day, I found out what was causing the defected reading and throwing off the controller..
R.F. around it causes the thermo coupling circuit to register higher readings and forces the controller to throttle back. My guess is it may have something to do with the ring near the tip that handles the seebeck circuit.
The R.F. source is a repeater in the 440Mhz range near by, just over my head. Lately, it has been very active in our locality.
I will need to investigate more, the type of input it is using. Something tells me it could be monolithic in nature and the front end maybe rectifying the signal?
Probably right on. Bipolar op-amps are notorious for rectifying RF signals and converting it to a some uV of DC. 20 degrees C on a type K thermocouple would be around 850uV. It can usually be reduced to a uV or two with careful filtering and design of the input circuit, but I suspect solder stations have the goodness Muntzed out of them to save a few pennies on ceramic caps and such like.
Best regards, Spehro Pefhany
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Discrete low-power AF stages are also prone to that effect. In my town (NE India), the P.A. system in some churches have experienced serious interference from the local AM transmitter, particularly in the past when many churches could afford only cheap PA sets, most of them installed by local youth. It doesn't seem quite appropriate to have the pastor deliver a sermon to the accompaniment of GnR or Lady Gaga. The solution I came up with was to insert an LPF or an LC circuit tuned to the AM station between the mic jack and the amplifier input. Some churches in certain rural areas are also complaining about inteference from Chinese and Bangladesh stations.
On a sunny day (Mon, 21 May 2012 02:03:38 +0530) it happened "Pimpom" wrote in :
Right, in Amsterdam we had the tram drivers radios break into the PA. I did the same, added LC low pass to all inputs of the mixer, also to the power line input. That fixed it.
Ferrite beads help a lot. This gained us about 30 dB in a thermocouple amp...
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mostly by damping hi-Q resonances in the box and wiring. You might try some of the clamp-on types on i/o wires. They are easy to install.
Here in San Francisco, the Planning Commission sits in ornate splendor, no expense spared. But the PA system makes horrible pulsing bleeping sounds from cell phones. It's been like that for years.
In my old ratty Fiesta, driving near Sutro Tower, the radio would make nasty noises even when it was turned off.
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John Larkin Highland Technology Inc
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Precision electronic instrumentation
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Intersting..NOT a common-mode damping choke AKA common mode resistive lossy device.
Typical politicos that have an infinite source of (taxpayer) money; too stupid to have it fixed.
Knew an engineer that worked in one of the TV stations there..complained that a Simpson VOM would not work most of the time, and a SexTronic scope was totally useless.
Yeah, exactly what i thought, but gave you benefit of doubt (possibility that maybe that form factor is available in lossy ferrite). Balun ferrite is not exactly known as being lossy, as the idea is to have MINIMUM insertion loss and over a wide band. So, presuming that works so well, what frequency range is it that is being adsorbed (turned into heat due to loss)?
I was RF testing this controller and found some sharp resonant responses in the 150 MHz sort of range. We plucked this core out of a Fair-Rite sample kit and popped it in, and it improved things roughly
30 dB. True, it's probably not a deliberately lossy ferrite, but it sure works.
I don't know that it's actually ohmic loss that's helping... maybe it's just the series inductance.
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John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Those are most often type #43, which has reasonable permeability up to a few megs, but a fairly broad resistive band out into 100-200MHz. Same material is typically used for "medium frequency" EMI parts.
Tim
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Been ages since i fiddled with ferrite baluns, I would bet on the series inductance. This is an accidental discovery that can be very useful for EMI control. Everyone should put that into their bag of tricks and give credit where credit is due. To any objectors, a classic case of an accidental discovery making billions of dollars was in the vulcanization of rubber.
Interesting. Type 43 is not noted for its loss, just for its bandwidth at normal levels. So.."series Inductance" is the winning vote. President Beadz the winnah!
Translation is at the end of this copy-and-paste from the mfgr: Part Number: 2873002402 Generic Name: Frequency Range: Suppression Applications for Lower Frequencies < 50 MHz (73 material) Description: 73 MULTI-APERTURE CORE Application: Suppression Components Where Used: Board Component Part Type: Multi-Aperture cores Preferred Part: Part Type Information Multi-aperture cores are used in suppression applications and in balun (balance-unbalance) and other broadband transformers. They are also employed in airbag designs to prevent accidental activation.
? All multi-aperture cores are supplied burnished.
? Multi-aperture cores in 73 and 43 materials are controlled for impedance only. The 61 NiZn material is controlled for both impedance and AL value. The high frequency 67 material is controlled for AL value. All listed impedance values are typical values. Minimum impedance values are specified for the + marked frequencies. The minimum guaranteed impedance is the listed typical impedance less 20%.
? Multi-aperture cores in 73 and 43 material are measured for impedance on the 4193A Vector Impedance Analyzer. The 61 multi-aperture cores are tested on the 4191A Impedance Analyzer. All impedance measurements are performed with a single turn to both holes, using the shortest practical wire length.
? The 61 and 67 material multi-hole beads are tested for AL value. The test frequency is 10 kHz at < 10 gauss. The test winding is five turns wound through both holes.
? Performance curves for individual components can be viewed by clicking on the part number in the chart.
? Preferred multi-aperture cores are the suggested choice for new designs. Samples are readily available and orders have typically shorter lead times than other multi-aperture cores. For any multi-aperture requirement not listed here, feel free to contact our customer service group for availability and pricing.
? Our "Multi-Aperture Core Kit" (part number 0199000036) is available for proto type evaluation.
? Explanation of Part Numbers: Digits 1&2 = product class, 3&4 = material grade last digit 2 = burnished.
I was using them in the '70s in PA systems. The two hole ferrite core could be installed inside a Switchcraft A3F or A3M, as long as you were careful cutting the wire length & soldering the wires without damaging the core. I was buying them from Amidon.
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