Figure 2. Packing glands are used to seal industrial temperature probes, cables, or tubes, preventing leakage of gas or liquids and preserving vacuum or pressurized atmospheres within a vessel. The elastomeric materials used in the seal permit easy element adjustment and resealing. Depending on the type of industrial sealant, packing glands can be used for temperatures ranging from -400 F to 1600 F (-240 C to 870 C). Common Mounting Devices In most common installation situations, you will attach the thermocouple/RTD to a pipe, autoclave manufacturer, vessel or industrial furnace. The sensor portion of the assembly resides within the sheath that is inserted into the vessel, with the sensor element at its tip. This sheath is connected, usually through a sealed nippleunion-nipple to the terminal head (see Figure 1). In certain instances, the sheath will be inserted into a thermowell that has already been installed into the vessel. If additional sealing is needed to prevent the gases or liquids from leaking, you can replace the connection nipple and/or union with a sealing gland assembly (packing gland). The nipple-union-nipple arrangement is a fixed mount; a sealing gland provides an adjustable mount (see Figure 2). If you wish to adjust the immersion depth of the sheath in the vessel, you can simply untorque the gland, industrial slide the probe in or out to meet your needs, and retorque the gland. Metal-to-metal seals and stainless steel ferrules can also be used for fixed mounting, but once torqued, they do not permit future immersion adjustment. As previously noted, some situations require a spring-loaded assembly that pushes the sensor against the bottom of a thermowell to allow maximum heat transfer. Spring-loaded assemblies are often used in heat treat pro3 cessing to monitor the temperature of a piece of steel inside a furnace. The assembly pushes the sensor against the steel to ensure that the measured temperature is that of the steel and not the medium around the steel. Calculating the Immersion Depth The goal of any temperature sensor installation is to position the sensor where it will be able to measure the temperature of the medium of interest. In a pipe, this spot is usually toward the center third of the pipe. As the medium approaches the pipe wall, the pipe material tends to draw off heat and cool the substance to be measured. The sensor should also be installed far enough into the environment to ensure that the stem and mounting fittings do not create a heat-sinking effect and corrupt the data. The distance from the sensor tip to the vessel wall is called the immersion depth. A frequently used rule of thumb to determine the correct immersion depth for thermocouples is to make it 10 times the probe diameter. For example, a 1/4 in. dia. probe would be inserted 2.5 inches. For RTDs, the immersion depth should be seven times the diameter of the probe. When your application is characterized by high temperature, high pressure or high flow rate, pay attention to the immersion depth; the greater the depth, the stronger and stiffer the probe must be to avoid damage during operation. www.conaxbuf .conaxbuff conaxbuf@conaxbuff 716-684-4500 Fax: 716-684-7 4-7433 1-800-223-2389 · www.conaxbuf falo.com · conaxbuf@conaxbuf falo.com · 716-684-4500 · Fax: 716-68 4-7433