Robertshaw Capacitance Level Probes
These probes are used with Robertshaw RF and microprocessor based ON/OFF or continuous level controls for measuring applications involving liquids or granular materials.
When the probe is used with an ON/OFF (fixed level point) type, it may be installed in the vessel in either a vertical or horizontal position. If, however, the probe is to be used on a continuous level measuring application or on an application with a differential (such as Pump On/Pump Off), then it must be installed into the vessel in a vertical position.
Bent probes are available to allow the active length of the probe to be different from the installation direction. See "Bending Specifications."
When the process is a conductive liquid (such as water or sulfuric acid) and the vessel is non-metallic or non-metallic lined, a probe with a ground wire may be employed to provide a ground path to the liquid (second plate).
The liquid must be clean and free of foreign materials and be no more viscous than water.
The Robertshaw Level Measuring instruments have been designed so that they attach directly to the 1/2" NPT fitting on the top of the probe. Typically, these are either the complete transmitter housing or a conduit outlet box with a coaxial cable to the instrument. The 6-32 threaded fitting in the end of the probe rod accepts either a contact pin or a machine screw as required.
Model 740A/C-B General Purpose Probe
The Model 740A is a general purpose rigid probe for use with Robertshaw capacitance instruments. It is used for level measuring applications involving liquids or dry materials. Available either bare (non-insulated) or Teflon insulated for use in conductive solutions.
The Teflon electrode insulation has a Teflon wall thickness of 1/16" over a 7/32" 316 stainless steel sensing rod. The Teflon insulated probe is recommended for use on low viscosity liquids and low to medium density granular materials. (For abrasive or agitated products, see Robertshaw Model 728B Heavy Duty probes.)
The Model 740A Probe has been designed to ensure long, trouble-free life. Extra tight fitting Teflon insulation has been incorporated into the design of the Model 740A Probe series. This insulation is continuous through the total length of the probe including the gland with an internal stainless steel sheath over the Teflon inside the gland. If a seal should break down and allow leakage into the gland, this internal construction is such that the measurement will not be affected and reliable readings will continue.
The Model 740A Probe, except as noted, conforms to the requirements of the National Association Of Corrosion Engineers (NACE) specification MR0175-88 (Material requirements For Resistance To Sulfide Stress Cracking For Oilfield Equipment).
The Model 740C Probe is a Model 740A Probe that has been registered in Canada as a pressure containing fitting and bears the Canadian Registration Number (CRN). All specifications for the Model 740C, except as noted, are identical to the specifications for the Model 740A Probe.