AO8010 Series Radio Frequency Impedance Level Gauges

I. Overview

The AO8010 series is a general-purpose point control instrument suitable for most applications. The instrument consists of a circuit unit and rod or cable-type sensor elements, with sensors available in various materials and can be installed in a whole or split assembly. It is used for limit control and alarm functions.

II. Working Principle

Radio Frequency Impedance Level Control Technology is an advanced level control technology developed from capacitive level control technology, offering superior anti-adhesion performance (material that adheres to the sensor is called "adhesive material"), greater reliability, more accurate measurements, and wider applicability. The term "impedance" in "radio frequency admittance" refers to the reciprocal of electrical impedance, which is a combination of resistive, capacitive, and inductive components. "Radio frequency" refers to high frequency, hence the radio frequency admittance technology can be understood as a method of measuring admittance using high-frequency currents.

The key distinction between the point-of-load radio frequency admittance technology and capacitive technology lies in the use of three-terminal technology and the diversity of measurement parameters. The central terminal of the circuit unit is connected to the centerline of the coaxial cable, which is then connected to the central terminal of the sensor. Simultaneously, the shield layer of the coaxial cable is suspended at a very small yet extremely stable potential level, which is equal in potential, phase, and frequency to the measurement signal but electrically isolated from it. This is equivalent to the measurement signal passing through a "gain of 1" amplifier with strong driving capability, the output of which is connected to the shield layer of the coaxial cable, and then to the shield layer of the sensor. The ground wire is another independent conductor within the cable. Due to the aforementioned relationship between the centerline and the outer shield of the coaxial cable, there is no potential difference between them, hence no current flows, meaning no current leaks from the centerline. This is akin to there being no capacitance or the capacitance being zero between them. Therefore, the temperature effects of the cable, as well as the installation of capacitors, will not have any impact.

Regarding the issue of material buildup affecting the sensor, a new sensor structure is employed, featuring a five-layer concentric design. The sensor structure consists of: the inner layer is the central probe rod, the middle layer is the shielding layer, and the outer layer is the grounded installation thread, which are isolated by an insulating layer. Similar to the coaxial cable scenario, there is no potential difference between the central probe rod and the shielding layer. Even if the material buildup on the sensor has a lower impedance, no current will flow. The electronic instrument measures only the current from the center of the sensor to the opposite container wall (ground), as the shielding layer prevents the current from returning along the sensor to the container wall. Therefore, the current to the ground can only pass through the measured material to the opposite container wall via the sensor's end.

The U center probe = U shielding layer, the I center probe to the shielding layer = (U center probe - U shielding layer) × YL = 0. Although there is an electric potential difference between the shielding layer and the container wall, with current flowing between them, this current is not measured and does not affect the measurement results. This protects the measurement end from the influence of hanging material. Only when the material in the container actually rises to contact the center probe, can an measured current form between the center probe and ground through the measured material, and the instrument detects this current, generating an effective output signal.

Radio frequency admittance technology, by introducing measurement parameters beyond capacitance, especially resistance parameters, improves the signal-to-noise ratio of the instrument measurements, significantly enhancing the instrument's resolution, accuracy, and reliability; the diversity of measurement parameters also effectively expands the reliable application fields of the instrument.

Features of Radio Frequency Capacitance Level Gauge

No Maintenance: Unlike whirl, vibration bars, or other mechanical switches, its components do not cause clogs, breaks, damage, or wear, and do not require regular maintenance or replacement.

Anti-Adhesion Material: The Driven-shield electrical design allows it to ignore the effects of wall adhesion or sensor component adhesives, eliminating the need for regular cleaning or repeated adjustments.

Wide Application: Process temperature ranges from -183℃ to +815℃，pressure from vacuum to 100bar

Three-color indicator lights: Red light - alarm, green light - normal, yellow light - gauge failure, reflecting the gauge status in real time

Convenient electrical connections: Dual electrical interface design for safer and easier wiring

High Drive Capability: 500Ω between center and shielded end, 150Ω between shielded end and ground

Arc Protection: Built-in 1000V arc protection, surge control, and transient surge control to ensure the circuit unit operates normally without damage.

Simple Installation: The gauge can be mounted through the threaded opening or flange on the tank, allowing for either a whole or split installation. It's straightforward, convenient, and easy to adjust and troubleshoot.

Section 3: Applicability Range

1. Liquid: Conductive liquids and insulating liquids

2. Propeller Body: Conductive Propeller and Insulated Propeller

3. Granules: Grain, Plastic Sheets, Coal, etc.

4. Interface: Interface between two liquids with different medium constants

5. Powder: Plastic Powder, Cement, Fly Ash, etc.

IV. Performance Specifications

1. Output: DPDT Relay (Double Pole, Double Throw)

2 Contact Capacity: 250VAC: 1A with sense, 3A without sense

3. Power Supply: 185-255VAC, 50/60Hz; 95-135VAC, 50/60Hz; 19-29VDC (High Power 2W)

4. Resolution: 0.2pF or smaller

5. Repeatability: < 1mm (0.04") (conductive material) < 20mm (0.79") (insulating material)

6. Load Resistance: Center terminal to shield terminal: 500Ω; Shield terminal to ground: 150Ω

7. Alarm Method: Can be set on-site to HLFS (High Level Alarm and Fault Insurance) or LLFS (Low Level Alarm and Fault Insurance)

8. Alarm Light Outputs: Red - Level Alarm, Green - Level Normal, Yellow - Instrument Fault

9. Environmental Temperature: -40-~+75℃ (-40-~+167℉)

10. Response Time: <0.5 seconds

11. Delay Time: 1-55 seconds (optional)

12. Safety Fence: Built-in flow limiter, four-level pressure protection safety fence

13. Static Discharge Protection (for sensors): Surge Resistance up to 1000V

14. RF Shielding (Built-in Filter): This transmitter circuit offers protection against RF interference from other exposed sensor components, cables, or transmission lines with a power of 5W, originating beyond 1.5 meters (59") from the unit, ensuring the operating point remains unaffected even in conductive materials.

15. Probe Length: 0.5m (19.7") (Standard) - 0.1m (3.9") to 20m (787.4") (Optional)

16. Cable Length: 5m (197") (standard), 0.1m (3.9") - 50m (1968.5") (optional) > 50m (1968.5" - 100m (3937") (contact manufacturer)

17. Electrical Interface: Double M20x1.5 (or 3/4" NPT optional)

Process Connections: BSPT Threaded Installation (Standard, Optional NPT), Flange Installation (Optional)

19. Shell Protection: Compliant with IP67 protection standard

V. Transducer Specifications