Custom Engineering Tech Tips

1. Spring Loading:

To ensure contact of a temperature sensor with the bottom of a thermowell or to maintain contact directly against an object to be measured use a spring loaded sensor. Simply suffix the sensor part number with -HNSL for a spring loaded hex nipple fitting with 1/2" of probe travel. This option is an additional $15.00.

2. Bending radius of clad:

OMEGA's thermocouple sensing probes that are made with Omegaclad have a 2.5 times bending radius. Probes can be bent by hand, however, we recommend the use of a tube bender to avoid kinking the sheath or damaging the conductors. Probes can be supplied from the factory with bends. Consult Sales Dept.

3. Thermocouple types R,S and B & Alumina insulation:

For stability of noble metal thermocouples (platinum/rhodium) types R,S and B particularly at high temperature, high purity alumina insulators and protection tubes must be used for insulating and supporting the thermocouple wires. Thermocouple types R,S and B should never be inserted directly into a metallic protective sheath or tube; doing so will result in contamination of the platinum wires resulting in excessive drift of the thermocouple.

4. Alternative sheaths for corrosive environments:

Worried about the corrosive effects that an environment may have on a 304SS or Inconel 600 sheath material? Well, OMEGA now offers a 321 stainless steel sheathed clad in all calibration types standardly. We can also provide a 316SS clad as a special order. In addition, most common probe types can be provided with an outer protective sheath such as Hastelloy B and C, Molybdenum, Quartz, Titanium and others. Contact Custom Engineering for sizes and styles available.

5. Surface Temperature Measurement:

(#1) Making a surface temperature measurement? For best accuracy, be sure to use a probe specifically designed for this purpose -- one that has low thermal inertia with the ability to make intimate contact with the surface in question. OMEGA's 88000 Series Surface Probes are good examples of this construction.

6. Dual probe configurations:

(#2) Q: I only have room for one thermocouple probe in my process, but I want to have both a local readout as well as a remote display in my control room. Can I still do this?

A: Neither thermocouple, RTD, nor thermistor signals can be "split" to go to more than one readout; however, most OMEGA temperature probes can be made in a dual configuration. Dual probes generally hold the exact same outer dimensions as the single version and make retrofitting easy.

7. N type instead of K type to minimize drift:

Experiencing unacceptable drift of your K type thermocouple reading? After prolonged use at higher temperatures, K type thermocouples can experience some thermal emf drift mainly due to changes oxidation causes in the composition of the alloys. The Nicrosil-Nisil, or N type thermocouple material, exhibits only a fraction of the thermal electromotive force (emf) drift typical of the standard type K thermocouple. OMEGA offers a full line of N type Omegaclad probes, wire and related hardware. Consult Custom Engineering if you do not find your probe of choice offered with the N type calibration.

8. Immersion of beaded wire probes:

Beaded wire thermocouples and immersion. The use of beaded wire thermocouples for water immersion is a more difficult application than it may at first appear. Although PFA insulation will seal against water along the length of the lead wire,there is no easy way to seal the tip after the insulation is stripped back and the thermocouple bead is made. Epoxy, silicone and polyvinyl and PFA shrink tubings may be suitable barriers against moisture, but there is no guarantee that the junction between these materials and the wire insulation will not be compromised by water in an immersion situation. Your best bet for long term readings in a fluid would be a fine diameter Omegaclad metal sheathed probe, available in diameters as small as .010". Omegaclad fine diameter probes offer fast response, durability and are immersible over the entire sheath length. Starting at under $30, no lab or manufacturing facility should be without these versatile probes.

9. 3 Wire configuration for RTD's:

When specifying RTD sensors, we recommend using a three or four lead wire configuration. When connected to the appropriate instrumentation, both three and 4 wire RTD's provide a means for compensating for lead wire resistance. In the case of a two wire configuration, the lead resistance can cause inaccurate measurements, especially when long lead lengths are used. The three wire configuration is the most common wiring style, while a four wire configuration is typically used when very high accuracy is required.

10. PFA ferrules for adjusting compression fittings:

When your application requires you to adjust a compression fitting once it has been fastened onto a temperature probe you can use a PFA ferrule. PFA ferrules must be used in applications with no pressure or very low pressure with the maximum operating temperature not to exceed 400 degrees F. The advantage of a PFA ferrule is that it will not deform the probe sheath as does a brass or stainless steel ferrule which results in a permanent mount of the compression fitting.