Alicat control devices now available with Autotune

Monday, 25th November 2024

What is autotune?

Alicat autotune is in-situ control optimisation for Alicat Mass Flow Controllers (MFCs) or Pressure Controllers (PCs). It is a complex and proprietary algorithm implemented inside the device’s firmware that intuitively and easily helps users find optimal control gains. This allows a user of an Alicat MFC or PC device to optimise system performance to their criteria without having any PID control background or understanding of control gains and how they work.

How does autotune work?

The algorithm runs through a series of trials, opening the control valve to varied degrees to carefully characterise system behaviour and determine control gains to match based on the user’s configuration. Autotune monitors the process and valve drive in real-time at 1 KHz, allowing high-resolution data to feed into optimal control gain selection.

How can I use autotune?

The autotune feature can be turned on through the device’s main display within the Control menu. Alternatively, the feature may be accessed through easy-to-use serial commands, typically RS-232 or RS-485.

Why should I autotune?

Outside factors effect valve tuning to how it has been factory configured. These may include:

Pressure – changes in differential pressure across the valve change the flow characteristics of the valve and thus the gain.
Gas - switching to a gas with a much different density than Air will significantly change optimal control gains.
Plumbing - large restrictions downstream of the MFC can cause P2 to vary as backpressure builds.

Having autotune switched on will prevent external factors effecting the control response of your Alicat device.

Popular Control Devices

MC Series Mass Flow Controller

98+ Preloaded Gases and Gas Mixtures. 0.6% of reading accuracy on most devices.

PC Series Pressure Controller

Gauge and absolute pressures up to 3000 PSI / 207 Bar. Differential pressures up to 100 PSI / 7 Bar.

How should I configure autotune?

Within the CONFIG menu on the device there are options for the tuning speed, the maximum flow tuning is allowed to use and what closed loop control algorithm will be used for tuning.

There are five options available for the desired tuning speed which are:

Fastest: Perform optimisation to maximize the speed of response (minimise the control loop response time constant). A small amount of overshoot in the response is allowed.
Fast: Perform optimisation with some emphasis on a faster speed of response over versatile usage.
Versatile: Perform optimisation with some emphasis on versatile usage over the speed of response.
Most Versatile: Perform optimisation targeting the most versatile usage, which will have the slowest speed of response.
Goal: Optimisation can be provided goal for the response time constant. The resulting control response will have a time constant close to this value for the tested setpoints, if the system can support it.

The maximum flow limits how much flow the device will attempt to use.

The Loop Type allow the closed loop algorithm to be constrained to the selected value. Automatic allows the tuning algorithm to choose the best loop type for the system and may result in either PDF or PD2I being chosen.

When should I use autotune?

When a desire to optimise control behaviour for an exact process or application is required.
When control problems are found which need to be mitigated.
When control performance needs to be characterised (periodic process evaluation, preventative maintenance, system anomaly detection, process modelling).
When differential pressure across the valve significantly changes, or a gas with very different characteristics is selected versus what the instrument was previously tuned with (i.e., switching from Air to H2 or increasing pressure from 10 PSIG to 100 PSIG).
When significant restrictions exist in the plumbing which creates a varying P2 outlet pressure.
When a process to move at a certain speed (GOAL) for normalization purposes or to protect sensitive processes.

What else should I know about autotune?

Autotune is available on devices which have firmware 10v11+ or greater. Talk to our service department today to see if your device has this feature available or can be upgraded to have this feature.

Premier Control Technologies are an approved Alicat service centre and are able to calibrate and service your Alicat device.

Well done for getting this far in this article, we also have a useful video below which shows the feature in greater detail:

MFC Autotune - Video demonstration

How does a Pressure Controller work?

Get in touch

If you have any questions about the Autotune feature, or in the Flow and Pressure control products in general please do get in touch on sales@pctflow.com or call us on 01953 609930.

Posted by James Kybird, Managing Director

Applications

Alicat control devices now available with Autotune

What is autotune?

How does autotune work?

How can I use autotune?

Why should I autotune?