Troubleshooting or repairing an Alicat device

Troubleshooting or repairing an Alicat device

Alicat 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. Many problems can be fixed without having to return the device to the factory. This article covers common issues with Alicat devices, and outlines solutions.

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

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

Troubleshooting your device

Downloading device registers

When troubleshooting an Alicat device, it can be helpful to first download all of the device registers and verify the current configuration.

Resolving error codes

When an error occurs with your Alicat product, you will be shown an error code such as ADC, MOV, EPL, POV, TOV, and VOV.

Power and communication issues

Common issues include:

  • Display won’t turn on, or is dim/weak
  • Buttons won’t respond and “LCK” appears on the screen
  • Analog output indicates values lower than what appears on the display
  • Serially connecting a device to a computer
  • Computer cannot communicate with the device over a serial connection
  • Computer cannot find BB3 or BB9 multi-drop breakout boxes
  • FlowVision software errors

Incorrect gas selected

Alicat's Gas Select™ menu

Alicat’s Gas Select™ menu

Alicat devices can be used to flow over 98 gases and gas mixes, but it is important to verify that the correct gas is selected prior to flowing. Having the wrong gas selected will not cause any damage to your device, but all flow readings will be off by approximately the ratio of the viscosities of the two gases.

This is an easy issue to fix. All you have to do is multiply the readings by the ratio of the selected gas viscosity to the desired gas viscosity. To prevent the problem from occurring again, update the gas selection in the Gas Select™ menu.

Incorrect flow readings

Common issues include flow readings that…

  • Won’t settle
  • Are negative
  • Don’t change when flow changes
  • Jump to 0 at low flow rates
  • Don’t match another flow calibrator

Liquid ingress into a gas flow instrument

Gas flow controllers and meters are designed to flow only gases, but accidental liquid ingress into a gas flow device can happen in most environments.

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 using the front panel or serial communication. More often than not, what seems to be a non-functional unit is just a controller configured for the incorrect application.


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.

Repairing your device

Sometimes troubleshooting can’t fix the problem, and an Alicat device must be returned to the factory for repairs. The most frequently seen failures (and prevention tactics) are listed 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 provide erroneous flow rates.

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

Spiderweb contamination inside a 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 a 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.

Contact an applications engineer for additional support