Saturday, June 29, 2019

Mass Spectrometer Heaters

Mass spectrometry (or mass spectroscopy) is a technique of analyzing and identifying chemical substances by arranging gaseous ions in electromagnetic fields based upon their mass-to-charge ratios. A mass spectrometer is the instrument used in this analysis. Mass spectrometers operate according to a principle first discovered in 1898 by Wilhelm Wien, a German physicist, who determined that moving ions can be deflected by electromagnetic fields.


The mass spectrometers can be broken down into (5) basic components:
  1. The high vacuum system.
  2. The sampling system - the area is where the sample is conditioned and introduced.
  3. The ion source - the area is where the charged particle ion beam is produced.
  4. The analyzer - where the ion beam is separated into its components.
  5. The detector - where the ion beam separation data is collected.
Mass spec heater
A variety of heater used in mass spec.
Mass spectrometry is used for the identification of chemical elements to quantify their precise mass and concentration; for  analyzing organic and inorganic chemicals to detect small amounts of impurities;  analyzing complex organic material structure; determining chemical bond strength; and determining an unknown materials chemical and isotopic makeup.

Mass spectrometer heating elements, referred to as source heaters or gas line heaters, are used in mass spectrometers are used to turn the sample (typically in an aqueous or organic solution) into a vapor for analysis. The heaters are part of the sample conditioning system, prior to the analyzer and detector areas, where the vaporized sample is then bombarded by ionized high-energy electrons and analyzed.

Mass spec heater
An alternative design heater.
Heaters used in mass spectrometers are compact in design and provide a fairly high power density. They are fast responding and operate at temperatures up to 400 deg. C. They include internal temperature sensors for accurate control and limiting. While mass spec vary in form and fit, they all provide the same basic function -  as the energy source for the vaporization of the sample containing the atoms or molecules of interest.

BCE (Belilove Company-Engineers) is a leading manufacturer of electric heating elements for mass spectrometers. With decades of experience in custom engineering and design of heating elements for analytical instrumentation, they are an excellent candidate to discuss the unique needs of your application.
Mass spec heater
Yet another style mass spec heater.

BCE
510-274-1990

Tuesday, June 18, 2019

The Operating Principle of Thermocouples

When two dissimilar metal wires are joined together at one end, a voltage is produced at the other end that is approximately proportional to temperature. That is to say, the junction of two different metals behaves like a temperature-sensitive battery. This form of electrical temperature sensor is called a thermocouple:



This phenomenon provides us with a simple way to electrically infer temperature: simply measure the voltage produced by the junction, and you can tell the temperature of that junction. And it would be that simple, if it were not for an unavoidable consequence of electric circuits: when we connect any kind of electrical instrument to the thermocouple wires, we inevitably produce another junction of dissimilar metals. The following schematic shows this fact, where the iron-copper junction J1 is necessarily complemented by a second iron-copper junction J2 of opposing polarity:


Junction J1 is a junction of iron and copper – two dissimilar metals – which will generate a voltage related to temperature. Note that junction J2, which is necessary for the simple fact that we must somehow connect our copper-wired voltmeter to the iron wire, is also a dissimilar-metal junction which will also generate a voltage related to temperature. Further note how the polarity of junction J2 stands opposed to the polarity of junction J1 (iron = positive ; copper = negative). A third junction (J3) also exists between wires, but it is of no consequence because it is a junction of two identical metals which does not generate a temperature-dependent voltage at all.

The presence of this second voltage-generating junction (J2) helps explain why the voltmeter registers 0 volts when the entire system is at room temperature: any voltage generated by the iron-copper junctions will be equal in magnitude and opposite in polarity, resulting in a net (series-total) voltage of zero. Only when the two junctions J1 and J2 are at different temperatures will the voltmeter register any voltage at all.

For more information about thermocouples (or any temperature sensor), contact BCE. They can be reached by calling 510-274-1990 or by visiting their web site at https://bcemfg.com.

Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.