Robershaw Capacitance Level products
Model 167 4-20ma Level Transmitter
The can be used to measure the level of liquids and solids in a variety of tanks, bins, totes etc. These products are based on measuring the capacitance between a probe and the wall of the vessel. These are also classed as RF ( Radio Frequency) Admittance, RF Impedance level measuring devices. Robertshaw provide Control Units and Probes for Single Point, Multipoint ( two points on a single probe ) and Continuous ( 4-20ma current output). The continuous level measurement can be used with 4-20ma alarms to generate multiple alarms from a single probe. Units are avalable with general purpose enclosures and explosion proof enclosures for hazardous areas.
These units all require a capacitance probe to operate. See Probes
Robertshaw Model 167 Level Transmitter
The Robertshaw Model 167 is an RF Capacitance to Current
transmitter producing a standard 4-20 mADC current output signal directly
proportional to the input capacitance. The Model 167 represents a totally
new concept in capacitance instrumentation and features a patented circuit
design to eliminate the effects of sensing probe coatings and provide a
true level signal. This circuit design operates on the admittance
principle such that all parameters are taken into account, such as
susceptance and conductance.
The Model 167 offers various supply configurations. The Model 167-A is a two-wire system operating on any DC voltage ranging from 17 VDC to 35 VDC maximum. This system allows for simple, inexpensive installation since only two standard wires are used to power the instrument and also carry the output signal. The Model 167-B/C series are four wire instruments utilizing 120 VAC or 240 VAC supply power.
FEATURES AND BENEFITS
- Two or Four Wire versions available - Simple, low cost, installations.
- Operates on Admittance Principle - Minimizes error due to material build-up on probe.
- Reverse Polarity, Lightning and EMI Protection - Tolerates long-lead wire runs without problems.
- Non-interacting and Wide Adjustability of Zero and Span - Simplifies initial calibration.
- CSA Certified Explosion-Proof and NEMA 4 Enclosure - Usable in Hazardous and Water-tight areas.
- CSA Certified Intrinsically safe models when used with approved barriers.
- Plug-in Circuit Boards - Ease of maintenance.
Standard features of the Model 167 include the "AntiCoating" feature, plug-in circuit boards for ease of maintenance when required, EMI suppression, lightning protection and reverse polarity protection on the two-wire version. The Model 167 is housed in an explosion-proof cast aluminum enclosure suitable for hazardous areas or Water-tight NEMA 4 locations. Due to the very low energy levels imposed on the sensing probe, as well as the low stored energy within the circuitry, the Model 167-A also qualifies as intrinsically safe when used with an approved safety barrier.