Maintenance and troubleshooting of ENOTEC SILOTEC 8000 silo analyzer

Maintenance and troubleshooting of ENOTEC SILOTEC 8000 silo analyzer

System positioning: O2/COE analysis for bin smoldering monitoring

SILOTEC 8000 is an O2/COE analysis system designed specifically for storage containers such as silos, coal bunkers, and biomass silos. It continuously extracts gas from the top space of the silo, while measuring oxygen content and CO equivalent, for early identification of smoldering fires. When smoldering occurs in the silo, the generation of hydrocarbons and CO consumes oxygen, resulting in an increase in COe concentration and a decrease in O2 concentration. SILOTEC 8000 can quickly capture this change and provide critical signals for safety interlocking, inerting protection, or alarm.

The system consists of electronic unit SME-53, measuring cell SIL-KES-0001, gas sampling probe SIL-GSF-8000, pneumatic unit, and GRP protective box. The electronic unit can be installed in a safe zone, and the measuring cell and sampling probe can be installed on the top of the silo, suitable for ATEX Zone 22 area. The sampling probe can extend into Zone 20. The maximum working pressure of the system is 0.5 bar, the maximum process gas temperature is 100 ° C, and the ambient temperature is -20 ° C to+55 ° C.

Measurement Principles and Safety Boundaries

SILOTEC 8000 adopts in-situ extraction measurement. The sampling probe is equipped with a sintered metal filter with a filtration accuracy of 3 μ m, which can safely isolate the explosive environment of dust in the silo from the heating sensor. The extraction system generates a continuous sample gas flow rate through an air injector, with a fast reaction speed. If equipped with a blowback module, compressed air can be used regularly to blow back the filter and reduce blockage.

Simultaneously install O2 sensors and COe sensors in the measurement pool. The O2 sensor is based on the zirconia principle, with instrument air (20.95% O2) as the reference side and sample gas as the measurement side. The difference in oxygen partial pressure on both sides generates an mV signal, which is converted to oxygen concentration using the Nernst equation. The COe sensor adopts the MXP principle and can detect CO, H2, and CxHy hydrocarbons. The catalytic electrode oxidizes incompletely oxidized gas molecules, generating a voltage signal related to the concentration of COe.

The safety boundary must be strictly adhered to: the system must not be used near flammable gases, otherwise there is a risk of explosion. The COe sensor requires a minimum of 0.3% O2 to measure correctly, and accuracy decreases below this value. The surface temperature of the measuring pool and the inlet and outlet of the sample gas may exceed 100 ° C. Insulated gloves must be worn during maintenance, and the power supply to the electronic unit must be cut off first. The measuring tank shall not be disassembled until it has cooled to below 35 ° C. It is absolutely forbidden to directly connect the probe to the 230V main power supply, otherwise it will immediately damage the heating element.

Installation and wiring points

The installation of electronic units should avoid vibrations greater than 2g and maintain a minimum distance from adjacent objects: 200mm at the top and bottom, and 50mm on the side. The ambient temperature must be between -20 ° C and+55 ° C, with a protection level of IP66. The installation position should be convenient for observing the display screen and operating the keyboard, and it is recommended to install it at a visual height.

The shielding layer of the probe signal cable FEP-0007/8 can only be connected to the PE terminal at the electronic unit end, and the probe end must not be grounded. The maximum length of the cable is 50m, the minimum bending radius of FEP-0007 is 252mm, and FEP-0008 is 329mm. The installation temperature is -5 ° C to+50 ° C, and the operating temperature is -40 ° C to+90 ° C. The signal cable should intersect perpendicularly with the power cable to avoid parallel wiring. The ferrite magnetic ring must be installed according to the specified wiring harness, otherwise the CE certification will be invalidated.

Pneumatic cable FEP-0002 is used for reference air and test gas, with a minimum bending radius of 138mm. When connecting, use a support sleeve, clamping ring, and nut, tighten by hand first, and then use a wrench to tighten 1.25 turns. The sampling probe flange needs to be air tight welded, and the filter locking torque is 250Nm. The electronic unit PE must be connected to the bin PE potential by the customer.

When wiring, please note that the O2 measuring cell, thermocouple, heater, probe solenoid valve, and COe sensor correspond to different terminals and colors. Thermocouple compensation cables must use ENOTEC original cables, otherwise the measurement will be inaccurate. COe sensor wire number 11-14, O2 sensor signal wire is white/brown and orange, heater is black/blue/green yellow.

Initial power on and software configuration

Before powering on, check whether the system number is consistent, whether the nameplate voltage matches, whether the wiring is correct, whether the gas circuit is airtight, whether the flange leaks, and whether the on-site conditions are consistent with the data sheet.

After turning on the power, the system prompts to select language, set date and time, enter TAG number, ENOTEC Remote password (if enabled), and probe cable length. The cable length must be accurately inputted, as incorrect length can lead to measurement deviation and even damage to the COe sensor. Then enter the heating stage: the O2 sensor is heated first, and after reaching 800 ° C, the COe sensor begins to heat up. The display screen shows the current temperature, set temperature, heating power, and waiting information.

In measurement mode, the screen displays O2 and COe measurement values, active range, trend bar, and limit alarm indicators. Three LEDs respectively indicate alarm (orange), maintenance (orange), and error (red). The keyboard has four soft keys and numeric keys. The system code is set to 0000 at the factory, so there is no need to enter it to enter the menu. For safety reasons, modifications should be made and saved properly. If the code is lost, only trained service personnel can perform a system reset.

Calibration menu and automatic calibration

SILOTEC 8000 supports 1-point calibration and 2-point calibration, which can be performed separately for O2, COe, or both simultaneously. One point calibration uses test air (20.95% O2) to determine the offset. Two point calibration uses test air and test gas to determine offset and slope. Calibration can be manually initiated in CAL-MENU, or automatically calibrated with ACAL timing or remotely triggered.

ACAL settings are only visible when enabled. The calibration method can be either 1-point (test air only) or 2-point (test air+test gas). The startup methods include: time triggered, time+digital input, and digital input. The digital input requires a 12-24V DC control voltage to be applied to the "calibration release" terminal. If the control voltage still exists after calibration, the calibration will immediately restart.

Before calibration, it is necessary to confirm that the test air and test gas flow rates are correct. The test air flow rate should be 60-80 l/h, and the sample gas extraction flow rate should be 40-80 l/h. For systems with traffic monitoring, traffic can be viewed in System Checks. Testing gas recommendation: O2 sensor should use 2.1% O2 to balance N2; COe sensor should use the gas specified in the test certificate. Test gas flow rate of 40-80 l/h, maximum inlet pressure of 3 bar.

During the calibration process, the display screen shows trend charts, current measurement values, flow rates, and progress bars. If the sensor signal is unstable, it will report "sensor calibration failure". At this time, the 'test gas application time' can be extended, with a default of 10 minutes at the factory and an adjustable range of 5-30 minutes. The pre blowing time is used to flush the sensor before 2-point calibration and is turned off by default. The delay time is used to maintain the final measurement value after calibration and display the trend.

Sensor replacement and measurement pool maintenance

Before replacing the COe sensor, the COe measurement must be set to OFF through software. Otherwise, the new sensor may be immediately damaged. Step: Turn off the COe measurement, cut off the system power, disconnect the gas circuit and electrical connections of the measurement cell, remove the insulation layer of the measurement cell, loosen the COe sensor lock nut, remove the clamping ring, O-ring, and retaining ring in sequence, and take out the old sensor. Be aware that the sensor may experience high temperatures.

When preparing a new sensor, insert the clamping ring, O-ring, retaining ring, and locking nut, paying attention to the inclined surface facing the O-ring. Insert the new sensor and tighten the locking nut. The system needs to be tightened again after running for 2 hours. Reconnect terminals 11-14, power on, and enable COe measurement. The software will ask if the sensor needs to be replaced, and after confirmation, enter the test certificate parameters: COe RH0, Offset, Alpha, Beta, Gamma, Delta, SO2 correction value. The RH0 value must be correct, incorrect values will immediately damage the sensor. If there is an input error, immediately close and restart COe measurement.

When replacing the O2 sensor or probe tube, first remove the measuring cell, take out the inner core, remove the filter head and test gas distributor, loosen the flange screws of the measuring cell, and remove the old sensor. Clean the flange, install new sensors and gaskets, reinsert the inner core, and ensure even spring pressure. Perform 2-point calibration under process conditions 24 hours after installation.

When maintaining the measuring pool, pay attention to the hot surface. Disconnect the power supply, remove the insulation layer, loosen the fixing screws of the tank body, and take out the measuring tank. If the COe sensor is removed for a long time, the guide tube must be sealed with a locking rod and sealing kit to prevent false air from entering. The filter inspection is carried out according to the process cycle, checking the sealing and locking nut, with a torque of 250Nm. The blowback module can be automatically triggered when the extraction flow rate is lower than the alarm value, or it can be started during calibration or sensor inspection. If the flow rate remains low for about 5 seconds after blowback, the system enters an error state.

Status messages and troubleshooting

The system error relay operates when there is a hardware error, thermocouple open circuit, O2 temperature not reached, temperature too low/too high, O2 sensor open circuit, calibration failure, low/high test gas flow rate, low/high offset, low/high slope, unstable signal, COe board communication error, COe heater short circuit/open circuit, COe sensor open circuit, COe board hardware error, COe calibration failure, invalid factor, remote module error, or sample gas flow rate error. The O2 signal output usually drops to 2.00mA, and the COe related error output is 20.80mA, unless otherwise set.

Common fault one: O2 display fluctuates greatly. Possible reasons include intermittent wiring and poor mV contact inside the probe. Solution: Check the wiring, eliminate looseness and disconnection. Common fault 2: O2 display stops at the end of the range or is too high. Possible reasons may be leakage in the sealing of the measuring probe or O2 sensor flange, or the probe flange not being air tightly welded. Solution: Check all flanges and threaded connections, replace O2 sensors or gaskets, and tighten flange bolts according to torque. Common fault three: Local display is correct but output is incorrect. Check the range setting, measure the mA output of the terminal, and determine if the electronic unit is faulty. Common fault four: O2 displays 0% but the expected process is high. Check the heater resistance (approximately 37.5-47.5 Ω), thermocouple resistance (approximately 2-80 Ω), heating fuse, cable short circuit or open circuit, probe core contact, and whether the measuring cell is damaged. If there is combustible gas present, it may form a reducing atmosphere and reduce the oxygen content on the sensor surface. At this time, it is necessary to be alert to the risk of explosion. Common fault five: high O2 and low COe. Usually, it is due to poor sealing at the coupling point of the COe sensor, causing ambient air to enter the installation pipe. Solution: Tighten or replace the COe sensor coupling component and recalibrate. Common fault six: No COe measurement value, displaying arrow. Possible beyond physical range or COe sensor malfunction. Perform O2+COe sensor inspection and check electrical connections. Common fault seven: No O2 measurement value, empty bar graph. The O2 value may exceed the coverage range of the electronic unit, such as under low O2 and high COe conditions. Perform O2+COe sensor inspection.

Quick check of technical specifications

Electronic Unit SME-53: Steel Powder Coated Shell, RAL6029， Optional GRP or stainless steel 19 inch rack. IP66， 19 inch rack IP20. LCD 240 × 64 LED backlight, thin film keyboard. The O2 range can be configured in two sections, from 0-2% to 0-25% O2, with an accuracy of less than 0.5% of the measured value or 0.02 Vol% O2. The COe range is 0-5000 ppm. Power supply 230V AC ± 10% or 115V AC ± 10%, 50/60Hz. Power consumption heating stage 425VA, measurement mode 225VA. Output O2 and COe are both 0/4-20mA active, maximum load 500 Ω, galactic isolated. Relay 24V AC/DC 1A, solenoid valve relay 230V AC/DC 1A. Size 300 × 440 × 240mm, weight approximately 19kg. Operating temperature -20 ° C to+55 ° C, storage -40 ° C to+80 ° C.

Probe SIL-KES-0001: Process temperature up to 100 ° C, immersion depth of approximately 500mm, process pressure ranging from ± 50mbar to atmospheric pressure. Environmental temperature -20 ° C to+55 ° C. Reaction time<1s, T90<5s. Material SS316, GRP transmitter housing, IP65， Applicable to Zone 22. The power is provided by the electronic unit.

Gas supply: Instrument air according to ISO 8573-1 Class 2, particle size ≤ 1 μ m, oil content ≤ 0.1mg/m ³, dew point pressure -20 ° C, inlet pressure 4-8 bar, O2 content 20.95%. Test gas 1 is instrument air or synthetic air. Test gas 2 according to the test certificate, with a maximum inlet pressure of 3bar and a flow rate of 40-80 l/h.