Troubleshooting vs. repairing an Alicat device

Troubleshooting vs. repairing an Alicat device

Alicat mass flow meters and pressure controllers are precisely engineered and rigorously tested. These devices are designed to maintain high accuracy calibrations while mitigating the effects of environmental factors. Because we believe it is important that our devices maintain performance after purchase, we have a team of Application Engineers to help customers get the most out of their instruments. In the event an Alicat device isn’t working as expected, we’re here to help identify and resolve the issue as quickly as possible.

If it ain’t broke… troubleshoot!

Many problems can be fixed without having to return the device to the factory. We’ve outlined some common issues and their solutions below:

Alicat's Gas Select™ menu

Alicat’s Gas Select™ menu

Incorrect Gas Selected

Alicat devices can flow over 98 gases and gas mixes, but it is important to verify that the gas selected on the device matches the gas used with the device. Flowing a different gas than selected usually won’t have any negative effect on the device itself. However, the measured flow readings will be off by approximately the ratio of the viscosities of the two gases. The data can be brought to near correct readings by multiplying each reading by the ratio of the selected gas’s viscosity to the desired gas’s viscosity.

To prevent the problem from occurring again, update the gas selection in the Gas Select™ menu as soon as possible.

Negative Flow Readings

A negative reading when there is no flow usually means the meter was flowing when it was last tared. To fix the problem, make sure there is no flow and give the instrument a fresh tare by selecting MENU > TARE from the home screen to correct the problem.

Tuning Issues

When an Alicat unit leaves the factory, the valve is configured to operate at certain standard conditions.  Sometimes these valve characterization conditions do not match the actual operating conditions. When this happens, it is possible the device won’t control with the speed or stability typical to an Alicat controller. Don’t panic! With Alicat devices, it is possible to change gains in the control algorithm from the front panel and via serial communication. More often than not what seems to be a non-functional unit is just a controller configured for a different specific application.

Having trouble troubleshooting?

We have a growing knowledge base online to make operating the instrument easier. However, some problems require more in depth knowledge on how the Alicat is (or isn’t) working. If that is the case, Applications Engineers are available to help by chat (in the bottom right corner of the page) or by phone +1.888.290.6060.

When it is broke… We’ll fix it.

Sometimes troubleshooting can’t fix the problem. For a variety of reasons, Alicat devices must be returned to the factory for repairs. To speed up a repair, include as much information about the failure or error and any troubleshooting that has already been performed so our team can focus on finding and resolving the issue.

The most frequently seen failures, how to spot them and how to avoid them in the first place are outlined below:


The most common service issue we see is contamination in the flow path. Without the proper precautions, foreign particles and debris collect in the valve and flow body and can cause the unit to clog or read erroneous flow rates.

Contamination can be as severe as a spiderweb inside the device.

Contamination can be as severe as a spiderweb inside the device.

To help prevent this, always clean fittings before installation and make sure to flow the appropriate gases from clean sources. We also recommend that appropriately-sized filters be installed throughout the process to protect against contamination.


Running the device at pressures beyond its specifications may damage the sensors. If the Alicat is reading strange values when no pressure is applied, it is possible that the sensor has been over-pressurized and is no longer functional.

To avoid damaging the sensor, always remember to use your Alicat device within the stated operating conditions. Refer to the device’s manual for these conditions. Exceeding them puts the Alicat device at risk of catastrophic failure

Electrical Issues or a Blown Transient Voltage Suppressor (TVS)

Failure to follow the correct power and communication specifications can result in catastrophic failure to the electronics in your device. Alicat devices contain TVSs to help protect the unit from power issues. Signs of blown TVS include anomalous voltage input/output readings to total loss of communication. If the device expresses one of these symptoms or seems to be pulling excessive current do not continue to operate the device.

To prevent electrical issues be mindful of what power source is being used to operate an Alicat device and take extra care to ensure wiring from the power source match the correct specifications.

Drifting Sensor Readings

All Alicat device readings will drift a little, well within specified accuracy. Drift is due to limitations of the sensor and is not cause for concern. To ensure accuracy of readings, always tare the Alicat device before use when the sensor is depressurized (and not in flow conditions).

If the device seems to be drifting more than the allowable specification, take note of flow and pressure readings at power up of the device and log these readings every five minutes for an hour. Deviation greater than 0.2% of the full scale range may mean that the sensor is defective.

Don't let this happen to your Alicat...

We’ve seen some pretty scary damage to a device. Proper care can help prevent damage.


To ensure that every device maintains specified performance and within warranty, we recommend annual recalibration of every Alicat device. By recalibrating annually, slight changes in flow readings that are within specification but are showing signs of drift can be corrected. It is also an opportunity to reconfigure the device to a new experiment or process, upgrade features and catch potential issues before they become problems.