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 1 -
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Question: The MFC control mechanism does not seem to work properly.
Solution : Check if the regulation is switched to analog or digital mode.
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| 2 - |
Question: The MFC does not seem to be linked or communicate properly.
Solution1: Check the communication speed by using the Digisoft software. Search for the menu “properties” and enter your PC communication speed.
Solution2: install the correct adapter.
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| 3 – |
Question: The MFC cannot be completely opened.
Solution: Check the inlet pressure and increase it if necessary.
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| 4 – |
Question: No flow value is shown.
Solution: Verify if the valves and gas panels are open;
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| 5 – |
Question: Is it possible to control the MFC processing ?
Solution: Launch Digisoft™ and 500 samples max can be processed and stored.
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| 6 – |
Question: I need to reduce the MFC Full Scale in order to get more accuracy.
Solution: Create an additional curve with Digisoft™ (Calibration slot index).
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| 7 – |
Question: The MFC seems to show oscillations.
Solution: Adjust RST parameters (calibration index of Digisoft).
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| 8 – |
Question: Is it possible to monitor my MFC ?
Solution: Yes, launch the alarm option in the Digisoft™ parameters.
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| 9 – |
Question: Can I control the MFC opening ?
Solution: Inside Digisoft™, enter ON for the ramping and the requested time value.
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| 10 – |
Question: The MFC shows a lack time when starting-up
Solution: Enter ON for the softstart and adjust the init valve for a regulation of 2%.
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| 11 – |
Question: The LVC ratio offset drift.
Solution: Purge the LVC and/or dismantle it in order to clean the cells.
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| 12 – |
Question: What is DeviceNet ?
DeviceNet is a low-cost communication link to connect industrial devices (such as limit switches, photoelectric sensors, valve manifolds, motor starters, process sensors, bar code readers, variable frequency drives, panel displays and operator interfaces) to a network and eliminate expensive hardwiring.
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| 13 – |
Question: What is a drift?
This a read out Offset measured at 0 flow that occurs due to the aging of the sensor.
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| 14 – |
Question: What are the units used for Flow Rates ?
Units for flow rate is usually displayed in terms of volume. The MFC converts mass flow into volume flow at 0 degrees C and 1 atm (101.32 kPa) to indicate flow per minute in either of the following units :
Standard centimetre cube per minute (sccm)
Standard litre per minute (slm)
1slm = 1000 sccm
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| 15 – |
Question: What is a wheatstone bridge?
 This is a Network electrical device used to measure a resistance X using three other known resistances P, Q and R.
X = R*Q/P
In a MFC, the Wheatstone bridge circuit electrically measures the heat loss in the sensor tube.
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| 16 – |
Question: What is a PID controller?
A controller with 3 gains so that the response is the sum of a proportional gain, an integrating gain and a differentiating gain.
A proportional controller (Kp) will have the effect of reducing the rise time and will reduce, but never eliminate, the seady_state error. An integral control (Ki) will have the effect of eliminating the steady-state error, but it may make the transient response worse. A derivative control (Kd) will have the effect of increasing the stability of the system, reducing the overshoot, and improving the transient response. Effects of each of controllers Kp, Kd, and Ki on a closed-loop system are summarized in the table shown below :
| Gain |
Rise time |
Overshot |
Response time |
S- error |
| Kp |
Decrease |
Increase |
Small change |
Decrease |
| Ki |
Decrease |
Increase |
Increase |
Eliminate |
| Kd |
Small change |
Decrease |
Decrease |
Small change |
GAIN RISE TIME OVERSHOOT RESPONSE TIME S-S ERROR
Kp Decrease Increase Small Change Decrease
Ki Decrease Increase Increase Eliminate
Kd Small Change Decrease Decrease Small Change
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| 17 – |
Question: What is the external readout?
Some of Qualiflow MFC include a jumper which makes possible to connect the meter part from the regulation part. The readout comes out from 2 pins: readout pin & external readout pin.
For a MFC with the "External Readout" option, the jumper is removed.
The measurement of the flow still comes out from the readout pin but the regulation is not done according to the flow but according to the signal coming from the "external readout " pin.
Typically the "external readout" is the signal coming from a pressure sensor and this gives a pressure controller.
The "external readout " input is basically located on the digital card internal connector and not on the SUB-D. This input goes directly to the ADC with no protection therefore if the "external readout " signal is outside 0-5V the card may burn out.
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| 18 – |
Question: What is the Cv?
The definition of Cv factor is the number of U.S. gallons of water per minute that will pass through a valve with a pressure drop of one psi at 60 o F (16°C). This is represented by the expression; Cv is equal to flow capacity in gpm times the square root of the ratio of the specific gravity and pressure drop in psi.
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| 19 – |
Question: What is the gas correction factor chart?
You can load it here.
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