Mass flow controllers allows us to precisely control the flow of gas, and is especially useful for experiments on olfaction and wind. This page contains way more information that you might need, but it maybe helpful if you see an unexpected behavior when using a MFC.
Choosing a model#
You can choose a max flow rate from a wide range of values. Note that for the Aalborg MFC, the accuracy is ~1% of the max flow rate.
If you only need to change the flow rate between trials, Aalborg will be sufficient (response time: ~1 sec). Note however that the response time depends on the flow with respect to the max flow rate. To be specific:
We specify response time for set point between 25 and 100% of full scale flow. If you start from zero flow conditions the response time will be much longer for set points below 25% of full scale. The lower your set point the longer it will take time to settle. This is derives from analog nature of the PID controller. With smaller difference between set point and actual flow the differentiator produce less signal and with fixed PID time constant (about 600 ms) it takes longer for current to reach point when valve start to open.
If you need faster fluctuations, you might need one from Alicat. Here’s an advice from Luis Hernandez Nunez in Aravi Samuel lab.
The advantage of using Alicat MFCs is that their rate of flow change is at least 5 times faster than the AALBORGs. The part number of the Alicat MFCs is MC-500SCCM-D and they need a power adaptor (PVPS24U). It is important to note that the part number depends on the specifications needed, the specifications that can be selected are shown here. For example you may need a different range of flow for your experiments, I use 0-500 ml/min for most of my experiments.
The AALBORG MFC I used for odor is this one. While the ALICAT MFCs are faster they might be more unstable than the AALBORG ones, I haven’t used the ALICATs long enough to make this claim though. I still keep the AALBORG MFCs for smooth signals, I got the ALICATs only for gaussian white noise experiments. The MFC for clean air doesn’t need to be fast, I use this one.
The one I got is Aalboarg GFC17A-VAL6-C0 with max flow rate 2L/min (~$1,000) and a 12V power supply . It’s important to choose the max flow rate wisely, as the precision is ~1% of the max flow rate. It’s possible to change this later but it costs a lot. (TO, 2021).
How to connect tubes to Aalborg MFC#
Recommended tubing for an Aalborg MFC. 1/4" OD copper tube with 1/4" compression fittings.
How to hook up an Aalborg MFC for external control#
In Aalborg MFC, you can set flow rate in two different ways:
- Local: you can turn the potentiometer on the side to set the flow rate.
- Remote: you can provide 0-5 V to control the flow rate (via NI-DAQ, for example). To set up remote option, see the pin configuration below.
- Please check first NJ1 valve configuration jumpers (see picture below). For remote 0-5Vdc option all jumpers except NJ1D must be on the top.
- For remote 0-5 Vdc option you have to make at least 4 wires connection on DB15 connector:
- Pins 7 and 5 for power supply.
- Pin 8 remote set point input (+) has to be connected to the remote source of 0-5 Vdc (+) terminal.
- Pin 1o remote set point input (-) has to be connected to the remote source of 0-5 Vdc (-) terminal.
- You should not connect anything to pin 11 when you are using remote 0-5Vdc voltage source.
This is what the NJ1 pins should look like for remote control:
How to hook up an Aalborg MFC for monitoring#
If you order the correct model, you will be able to record the flow rate as 0-5V signal.
Just hook up a connector to the pins 1 and 2 in the pin diagram above.
I have observed a high-frequency noise. According to Aalborg , it’s likely an electromagnetic interference (EMI) coming from solenoid valve current output, and the actual flow rate is not capable of oscillation with high frequency because the time constant of the valve is more than 25 ms. I used a simple RC low-pass filter (R = 1.5k ohm, C = 10 uF, fc = 10Hz) to filter the signal (top: before, bottom: after filtering).
