FT8051 series RF admittance deep well level gauge

The FT8051 series RF admittance deep well level gauge is based on the principle of RF admittance and adopts three terminal shielding drive technology. The instrument consists of a circuit unit and cable type sensing elements, and can be installed as a whole or separately. Mainly used for water level detection in deep water wells.

　　measuring principle

Radio frequency admittance level control technology is a level control technology developed from capacitive level control technology, which is anti hanging, more reliable, accurate, and widely applicable. The meaning of "admittance" in "radio frequency admittance" is the reciprocal of impedance in electricity, which is composed of resistive, capacitive, and inductive components. "Radio frequency" refers to high-frequency radio waves, so radio frequency admittance technology can be understood as measuring admittance using high-frequency radio waves. A high-frequency sine oscillator outputs a stable measurement signal source, utilizing the principle of a bridge to accurately measure the admittance of sensors installed in the container under test. In direct action mode, the output of the instrument increases with the rise of the material level.

The difference between radio frequency admittance technology and traditional capacitance technology lies in the diversity of measurement parameters, the driving three terminal shielding technology, and the addition of two important circuits, which are improved based on valuable experience in practice. The above technology not only solves the problems of cable shielding and temperature drift, but also solves the problem of hanging materials at the root of vertically installed sensors. The two added circuits are a high-precision oscillator driver and an AC phase detector sampler.

For a container made of highly conductive material, since the material is conductive, the grounding point can be considered to be on the surface of the probe insulation layer. For the transmitter probe, it only appears as a pure capacitor. As the container is discharged, material is hung on the probe rod, which has impedance. In this way, the previous pure capacitor has now become a complex impedance composed of capacitors and resistors, causing two problems.

The first issue is that the material itself is equivalent to a capacitor to the probe, which does not consume the energy of the transmitter (pure capacitor does not consume energy). However, if the equivalent circuit of the hanging material to the probe contains a resistor, the impedance of the hanging material will consume energy, thereby pulling down the oscillator voltage and causing changes in the bridge output, resulting in measurement errors. We have added a driver between the oscillator and the bridge to replenish the consumed energy, thus stabilizing the oscillation voltage applied to the probe.

The second issue is that for conductive materials, the grounding point on the surface of the probe insulation layer covers the entire material and hanging area, allowing the effective measurement capacitance to extend to the top of the hanging area, resulting in hanging errors, and the stronger the conductivity, the greater the error.

But no material is completely conductive. From an electrical perspective, the hanging material layer is equivalent to a resistor, and the part of the sensing element covered by the hanging material is equivalent to a transmission line composed of countless infinitely small capacitors and resistance elements. According to mathematical theory, if the hanging material is long enough, the impedance and reactance values of the capacitance and resistance parts of the hanging material are equal. Therefore, an AC phase detector sampler can be used to measure capacitance and resistance separately. The total capacitance measured is equivalent to the C level+C hanging material, and then subtracting the resistance R that is equal to the C hanging material, the actual value of the material level can be measured to eliminate the influence of hanging material.

characteristic

Intrinsic safety design: Two wire intrinsic safety design, where both the unit and probe are inherently safe

Maintenance free: No moving parts, no wear or damage, no need for regular cleaning, no need for repeated debugging

Anti hanging material: The Drive shield electrical design allows it to ignore the influence of hanging materials on walls or sensing components

No drift: Will not drift due to temperature or density changes in the medium

Reliable lifespan: Unique technology ensures instrument service life of up to 15 years

Safety protection: Built in probe input device, strong protection ability, not easily affected or damaged by static electricity, impact and electrochemical phenomena

Typical applications

Water level detection of deep water wells in oil fields

Groundwater level measurement and environmental protection testing around cities

Water level detection of power plant water source well

Water level detection of deep water wells in water plants

　　performance index

Measurement equipment level: CAT I level, transient rated voltage 1500V, cannot be used for levels other than CAT I level

Output: 4-20mA

Measurement method: can be set as level mode (DIR) or distance mode (REV)

Power supply: 15-35VDC

Power: less than 0.5W

Accuracy: ± 1%

Temperature effect: 0.25%/10 ℃ (18 ℉)

Load resistance: Output circuit load resistance capacity of 450 Ω at 24VDC

Environmental temperature: T5: -40 to+70 ℃ (-40 to 158 ℉); T6: -40 to+60 ℃ (-40 to 140 ℉) (The influence of medium temperature on ambient temperature cannot exceed the instrument's requirements for ambient temperature)

Response time:<0.5 seconds

Delay: adjustable from 0.5 to 80 seconds

Electrostatic spark protection (for sensors): anti surge impact 1000V, anti-static 4kV/8kV

RF protection (built-in filter): The whole machine is tested by injecting current through a 10V/m electromagnetic field and a 3V/m electromagnetic field in space

Measurement depth: up to 1000 meters (range 0-180 meters)

Cable length: 5m (standard) (197 "), 0.1 (3.9") to 50m (1968.5 ") (optional)

Consult the manufacturer for 50m (1968.5 ") to 100m (3937")

Electrical interface: M20 × 1.5 (optional 3/4 "NPT)

Process connection: NPT thread installation (standard, optional BSPT), flange installation (optional)

Process temperature: -20 to+120 ℃ (-4 to 248 ℉)

Process pressure: ≤ 1.6MPa (232psi)

Probe material: 304SS/PVDF

Shell material: die cast aluminum with epoxy coating

Shell protection: Compliant with IP67 protection standard

Explosion proof grade: ExiaICT4

Certification: PCEC/NEMSI. For other certifications, please consult the manufacturer

Probe indicators

FT8051 wiring diagram

The FT8051 series deep well water level gauge belongs to the intrinsic safety type instrument. Whether installed as a whole or separately, when installed in hazardous environments, a jointly certified safety barrier needs to be added to its power supply circuit. Both single and double barriers can be used, but the connection method is different. The examples in the intrinsic safety application system and safety barrier wiring diagram are single barrier integral installation and double barrier separate installation. For safety barrier products that have been jointly certified, please consult our company or our agent. The maximum impedance of cables, loads, and safety barriers under 24VDC power supply is 450 Ω.

Please refer to the instructions for the use of safety barriers for grounding requirements. The requirements for safety barriers in this level gauge are:

Uo=28VDC

Io=93mA

Po=0.65W

Co=0.083uF

Lo=4.2mH

Safety parameters of this instrument:

Ui=30V

Ii=100mA

Pi=0.75W

Ci=6nF

Li=240uH

Intrinsically safe application system and safety barrier wiring diagram

　　Installation requirements for FT8051

l. The installation, use, and maintenance of the product should comply with the relevant provisions of the product installation, commissioning, and use instructions, GB50257-96 "Code for Construction and Acceptance of Electrical Equipment in Explosive and Fire Hazardous Environments", GB3836.15-2000 "Electrical Equipment for Explosive Gas Environments Part 15: Electrical Installation in Hazardous Areas (excluding Coal Mines)", and GB3836.13-1997 "Electrical Equipment for Explosive Gas Environments Part 13: Maintenance of Electrical Equipment for Explosive Gas Environments".

When installing instruments, they should be kept as far away as possible from vibration sources, high temperature environments, corrosive air, and any places that may cause mechanical damage. If the requirements cannot be met, please replace the instrument with a new component. The ambient temperature should be between -40 and 70 ℃ (-40 and 158 ℉).

The instrument installation area requires lightning protection devices to prevent lightning strikes.

It is prohibited to use single component ambient temperature sulfurized sealant inside the instrument casing. This substance often contains acetic acid, which will corrode electronic components. Special two-component sealant (non corrosive) should be used.

The instrument casing is equipped with grounding terminals, and users should ensure reliable grounding during installation and use. When used for non-metallic cans, a standard ground should be provided on site and cannot be connected to the power ground.

The electrical interface should be equipped with cable sealing joints with a protection level of IP65 that meet the requirements of GB4208 standard to ensure reliable sealing and prevent damage to the instrument electronic unit caused by water ingress or other corrosive gases.

Do not disassemble the sensor or loosen the sealing nut to avoid probe leakage.

The installation of sensors should avoid material flow or inlet/outlet ports. If there are no other installation locations, protective covers or partitions should be added.

The installation of threads or flanges should be firmly connected to the container, reliably sealed, and have good electrical contact. Except for the connection, other parts of the sensor should not come into contact with the container to ensure good insulation.

When installing the sensor horizontally, it should be slightly tilted downwards at an angle of 10-20 °.

When installing hard rod sensors, the installation space should be considered, with a distance of at least 100mm from the tank wall. Cable sensors should be straightened after installation, with a distance of at least 300mm from the tank wall to avoid short circuits to the ground.

In situations where there is significant mixing, airflow, and material flow fluctuations inside the container to be tested, in addition to avoiding direct mechanical damage to the sensor, indirect mechanical damage such as long-term fatigue of the sensor material should also be considered. Therefore, it is recommended to install protective measures such as intermediate support and bottom anchor fixation for the sensor. Please note that the support and ground anchor should be insulated from the sensor, and the insulation material should be selected from materials with high insulation strength, low hardness, lubrication function, and no wear on the sensor (such as PTFE). If not, please consider replacing the sensor regularly to avoid sensor damage and chain loss.

When measuring large quantities of solid particles, the heavy hammer at the end of the sensor should be as high as possible above the cone angle of the silo. If it is necessary to enter the conical section, the maximum entry size should not exceed 20% of the diameter of the silo.

The non active section of the sensor should enter the tank at least 50mm. When the cable sensor is installed horizontally, the hard rod part entering the tank should not be less than 200mm, and when installed vertically, the hard rod part entering the tank should not be less than 100mm.

The instrument circuit installed according to intrinsic safety standards must be equipped with safety barriers certified by GB3836.1 and GB3836.4 explosion-proof standards.

The ripple of 24VDC power supply shall not exceed 100mV.

The instrument connection cable shall comply with the requirements of IEC60245/60227 standard. It is recommended to use armored shielded 3-core cables with an outer diameter of no more than 12mm. The cable conductor material is copper, and the cross-sectional area of the conductor is 0.13-2.1mm2 (AWG14-26). The insulation strength of the cable is 1500V. Long distance unshielded cables cannot be used in parallel with AC power cables.

When using and maintaining on site, the principle of "no opening with power on" must be followed, and it is recommended to shut off the power for 10 minutes before operation.