| Q1 |
What are differences between the usages of the MG8G model and MG8E model? |
| A1 |
The MG8G Paramagnetic Oxygen Analyzer is for general use and the MG8E Paramagnetic Oxygen Analyzer is for explosionproof applications.
The MG8E has been certified by the TIIS* to meet the Exd II BT4 standard.
* Technology Institution of Industry Safety, Japan
Selection of the model is mainly determined depending on whether or not explosion protection (flame-proofing) is required for your application.
The MG8E flame-proof model is used for applications that require a measurement range of less than 0 to 5 vol%O2, even when explosion protection is not required.
The following table shows the applicable criteria of the MG8G and MG8E.
Model MG8 Paramagnetic Oxygen Analyzers
(Installation Environment, Measured gas)
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| Q2 |
MG8G/MG8E Paramagnetic Oxygen Analyzers System Configuration |
| A2 |
The pre-treatment unit varies depending on the device and application, so all pre-treatment units have to be custom-ordered.
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| Q3 |
The condition of sample gas? |
| A3 |
| Sample gas temperature : |
to 50°C |
| Sample gas Humidity : |
No moisture condensation in the flow path or the sensor. |
| Sample gas Pressure : |
Approx. 7 kPa (approx. 700 mmH2O) in Analyzer inlet |
| Sample gas Flow : |
300 to 800 ml/min（MG8E）, 200 ml/min±10%（MG8G） |
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| Q4 |
Why is auxiliary gas necessary? |
| A4 |
The MG8G and MG8E Paramagnetic Oxygen Analyzers can be used not only to measure oxygen concentrations in gas mixtures including flammable gas, but also for a wide range of applications, such as to measure oxygen concentrations in corrosive gases. They are equipped with a magnetic proportional flow rate sensor that has been developed by Yokogawa.
The following figure shows the Principle chart of the Magnetic Proportional Flow Rate Sensor.
An auxiliary gas enters from the auxiliary gas inlet and is divided into streams B and B', which then pass through a thermistor that is positioned in each of the gas paths. These thermistors detect the flow rates of the auxiliary gasses.
The auxiliary gas streams then enter the ring-shaped path at points D and E, where they meet with the sample gasses and flow in direction C toward an outlet.
A strong magnetic field is created at point D, where stream B of the auxiliary gas enters the ring-shaped path. If the sample gas contains oxygen, the oxygen is attracted to and concentrated in the magnetic field at point D. The oxygen thus restricts the flow of auxiliary gas at point D, which alters the ratio of flow rate B to flow rate B'. This change in the ratio is proportional to the oxygen concentration, and it is detected with the thermistors and output.
Magnetic Proportional Flow Rate Sensor
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| Q5 |
Measurement range and output range setting |
| A5 |
| Measurement range : |
0 to 25 vol%O2 |
| Minimum output range : |
0 to 1 vol%O2 （MG8E）
0 to 5 vol%O2 （MG8G） |
| Maximum output range : |
0 to 25 vol%O2 |
Up to three arbitrary ranges can be set within the above range in vol%O2.
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| Q6 |
Can the output be held during calibration or when an error occurs? |
| A6 |
The output signal can be held at the last measured value or at a preset value during the warm-up period, during calibration, and when an error occurs.
The following table shows the relationship between the device status and the analog output hold values that can be set.
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| Q7 |
What are the contact inputs? |
| A7 |
Up to three contact inputs can be connected to the MG8G and MG8E Paramagnetic Oxygen Analyzers.
The contact input performs a preset function by receiving a dry (non-voltage) contact signal from the outside.
The following items can be set.
• Remote range switching :
2 points, Output ranges 1 to 3 can be switched by external contact signal.
Range 1 : Contact 1 Open、Contact 2 Open
Range 2 : Contact 1 Open、Contact 2 Closed
Range 3 : Contact 1 Closed、Contact 2 Open
• Calibration Start Contact Input : 1 point
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| Q8 |
What are the contact outputs? |
| A8 |
The following contact outputs are available for the MG8G and MG8E Paramagnetic Oxygen Analyzers.
| Fail : |
1 point, open or closed when error occurs, user configurable |
| Auxiliary gas pressure low : |
1 point, closed when pressure low |
| Maintenance status : |
1 point, closed during maintenance |
| Range answerback or high/low alarm : |
2 points, normally deenergized (open) |
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| Q9 |
Overview of calibration |
| A9 |
MG8G/MG8E Paramagnetic Oxygen Analyzers should be calibrated at two points using zero gas (nitrogen gas with an oxygen concentration of 0%) and span gas with a known oxygen concentration.
The following figure shows the relationship between the sensor output and the oxygen concentration.
The ratio of the oxygen concentration to the sensor output is calculated from the sensor output values (p1 and p2) obtained in calibration.
Assuming that the sensor output when sample gas is applied is ps, the concentration of the sample gas, cs, is obtained from the following equation.
Calibration is for obtaining k.
When only a zero calibration is performed, the instrument is calibrated to the zero gas's value and the
ratio of the oxygen concentration to the sensor output, k, that was obtained from the previous calibration, is used.
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| Q10 |
What are calibration operation modes and calibration time settings? |
| A10 |
The following three calibration operation modes are available for the MG8G and MG8E Paramagnetic Oxygen Analyzers.
Manual Calibration :
A zero calibration should be performed first, and then a span calibration by manual
Semiautomatic Calibration :
In the semi-automatic calibration, zero and span calibrations are carried out under the preprogrammed conditions using the calibration start contact input.
Automatic Calibration :
Calibration can be automatically executed for preprogrammed calibration times at preprogrammed intervals.
The following describes the calibration time setting and other items.
(1) In case of Manual Calibration
Setting stability time
The stability time refers to the time from when calibration is finished until measurement starts again.
Set the time from when calibration is finished and then the sample gas will be introduced to the sensor until the output returns to the steady state.
During the time from when the calibration procedure finishes until the output stability time elapses, the output remains in the state set in "Output hold." The setting range is from 0 to 99 minutes.
(2) In case of Semi-automatic calibration
In the semi-automatic calibration zero and span calibrations are carried out under the preprogrammed conditions using the calibration start contact input.
The amount of time for zero gas to flow. The timer starts when the solenoid valve in zero gas line opens to allow the zero gas to flow through the sensor unit. Set the amount of time it takes for the reading to stabilize sufficiently. The setting range is from 1 to 99 minutes.
The amount of time for span gas to flow. The timer starts when the solenoid valve in zero gas line closes and the solenoid valve in span gas line opens to allow the span gas to flow through the sensor unit. Set the amount of time it takes for the span gas to purge the zero gas in the sensor and for the reading to stabilize sufficiently. The setting range is from 1 to 99 minutes.
(3) In case of Automatic calibration
For the automatic calibration, the following should be set "For the zero calibration time", "Initial wait time", "Calibration interval", "Execution of span calibration", "The number of times of skipping span calibrations" and "Starting automatic calibration function".
Initial wait time :
The amount of time until the first calibration is executed after the automatic calibration function was started. The setting range is from 0 day 0 hour to 99 days 24 hours.
Calibration interval :
Set the time interval for automatic calibration. The setting range is from 0 day 1 hour to 99 days 24 hours.
Execution of span calibration :
Set whether or not to execute span calibration.
The number of times of skipping span calibrations :
The number of times of skipping span calibrations can be set only when "1" is set in Function. The setting range is from 0 to 99 times.
Starting automatic calibration function :
Set to "1" to start the automatic calibration function. After the set initial wait time has elapsed, the first calibration starts.
The following figure shows the timing diagram when the number of times of skipping span calibrations
is set to "2."
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| Q11 |
Measurement of Oxygen (O2) in the Presence of Interference Gases |
| A11 |
MG8G/MG8E Paramagnetic Oxygen Analyzers make use of the paramagnetic property of oxygen (magnetic susceptibility, i.e. the ability to become magnetized in the presence of an externally applied magnetic field) to measure the oxygen concentration. Gases other than oxygen may also exhibit this characteristic, although they will not be nearly as magnetically susceptible as oxygen. Accordingly, process gases with varying levels of magnetic susceptibility can interfere with and cause errors in the measurement of the oxygen concentration.
Errors such as these that are caused by the paramagnetic property of process gases may be significant with low oxygen concentrations in the range of 0% to 1%; however, the MG8G/MG8E Paramagnetic Oxygen Analyzers are able to cancel out this interference error based on the difference in density of a sample gas and a reference gas.
Prior to shipment from the factory, each MG8G/MG8E Paramagnetic Oxygen Analyzer receives a final tuning in which the measurement cell angle (attitude) is adjusted based on the magnetic characteristics and density of the customer's sample gas. This cell angle is stored in the analyzer's memory.
When installing the analyzer, rotate the adjustment knob until the bubble in the built-in bubble level is at the center position. This brings the measurement cell to the correct angle.
The following table indicates when the MG8E analyzer can be used to measure oxygen (O2) in the presence of interference gases.
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| Q12 |
How is error diagnosis performed? |
| A12 |
The types of errors detected by the self-diagnostic function and remedies are summarized in the following table.
When an error occurs, the FAIL lamp turns on and the Fail contact is activated.
As for the calibration coefficient error, the FAIL lamp turns on and the Fail contact is activated only when semi-automatic or automatic calibration function is enabled.
Errors and Remedies
| Error type |
Error
code |
Description |
| Sensor unit error |
E-10 |
Sensor emf continues to exceed 400 mV for at least 10 seconds. |
| E-11 |
Sensor emf continues to fall below -50 mV for at least 10 seconds. |
| Constant temperature chamber error |
E-20 |
In stabilization period or steady state, heater temperature
continues to fall below 50°C for at least 10 seconds. |
| E-21 |
In stabilization period or steady state, heater temperature
continues to fall below 60°C for at least 10 seconds. |
| E-22 |
In warm-up period, heater temperature
fails to rise. |
| E-23 |
In warm-up period, heater temperature continues to exceed 65°C for at least 10 seconds. |
| Analog error |
E-30 |
Failure occurs in A/D converter on circuit. |
E-31
E-32
E-33 |
Voltage of sensor unit exceeds input range of A/D converter. |
| Memory failure |
E-40 |
Failure occurs in memory device on circuit. |
| Calibration coefficient error |
E-50 |
Zero calibration coefficient is outside of ±1.25% O2. |
| E-51 |
Span calibration coefficient is bellow 0.9 or above 1.09. |
| Atmospheric sensor error |
E-40 |
Atmospheric sensor output exceeds the normal range. |
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