heater_control

The heater controls for the MAG Laboratory natural gas heater

Branch Description

This is the "zero" branch where the initial development is supposed to take place.

Future Work

This program may need to be converted to use the TCP version of modbus since there are supposed to be multiple devices on this bus.

Additionally, the (kick) start timer may be improved if there is a linear rise in the low-limit so that the script can more precisely track the set point temperature.

Description

This software consists of a few components which enable a user to interact with a simple HMI which can set parameters and contains an internal relay to activate the heater.

One can simplify this to a set of components:

• MQTT sensor input
• occupancy calculation
• heater control algorithm
• user interface
• heater output

User Interface

The user interface accepts input from the buttons on the HMI and allows access to several parameters. There is a separation between three categories of parameter:

• Read-only
  • Temperature
• Numberic
  • Set-Point
  • Filter Ratio
  • Hysteresis
  • Start Time
  • Occupancy Cold Time
• Binary
  • Force occupancy
• Save

Heater Control Algorithm

The heater control algorithm is a bang-bang control algorithm developed with empirical data and a filter.

The high-point is set at the set-point and the low-limit is set at the set-point minus hysteresis unless the (kick) start timer is expired.

The heater is turned on at the low-limit which is based directly on the measured temperature.

The heter is turned off at the high-limit which is based on the filtered temperature.

The Filter

The filter uses the classic floating point infinite impulse response (IIR) filter. The user can choose the filter ratio (or alpha) from the user interface.

$$y[n] = (1-\alpha) y[n-1] + \alpha x[n]$$

(kick) Start Timer

The timer starts when the heater turrns off. Upon expiration of the start timer, the low-limit is set to half of the hysteresis value.

Occupancy Determination

The occupancy of the makerspace is determined using a state machine.

This state machine has three states and begins with the Cold state:

• Cold
• Warm
• Hot

The state transitions from the Cold state to the Hot state if there is more than one active motion sensor.

The state transitions from the Hot state to the Warm state automatically.

The state transitions from the Warm to the Hot state if there is at least one active motion sensor.

The state transitions from the Warm to the Cold state if the state machine has remained in the Warm state for too long.

The output of this state machine is binary:

• True if the state is not Cold
• False otherwise

Dependencies

• pago-mqtt
• dataclasses-json
• minimalmodbus

Installation

This script can be "installed" using the included systemd .service and environment file.

The current configuration code allows for this script to be installed at /usr/local/bin and its configuration to be stored in /etc.

Help

Please do not hesitate to leave a Github issue or email the default MAG Laboratory contact [at] maglaboratory.org.

Authors

• @blu006

Version History

• TODO: first released version

License

The Unlicense