How does Haystack handle the concept of the actual status of a device, equipment, etc. There are many instances where a current switch, differential pressure switch, etc are used to measure the actual status of a piece of equipment. Displaying the command of a fan for example is not enough. You need to know in many cases what the fan is being told to do, but it is equally important to know what the fan is actually doing.

Brian,

If we take your fan example, we have the command we are sending to the fan and we have a sensor using to determine if the command is actually running. We might have similar command/sensor pairing for dampers, pumps, etc. In this case we just create two points and pair the cmd and sensor tags. For example:

// actuator command point for fan
discharge fan cmd equipRef: <AHU-2 Fan-Cmd>

// differential pressure of fan
discharge fan sensor equipRef: <AHU-2 Fan-DiffPres>

Also take a look at fan docs to see how this is described.

This is my first post here so excuse me if it appears out of order ..I think I can see what Brian Turner is asking here. The example given above refers to a differential pressure "sensor" for fan status feeedback. A sensor (transmitter) might appears as an analogue input and therfeore a feedback of "Run" or "Stop" is not valid without some logical extension of the pressure value.

In the sensor tags it seems we can define the BI types (in this example discharge/air/pressure/ switch, however when I examined the units section of the documents I was unable to find any contents associated with a status point. Is there going to be such definition or are the boolean units going to remain simple (true/false), if not then I can see where Brian Turner is going with this we can command a fan to "start" and the Fan pressure SWITCH goes "true" giving us the "run" feedabck status.

I thought I actually answered this question. What the actual specification for the fan tag says follows. Let me know if this doesn't fully cover the use case or doesn't make sense

If annotated as an output with the cmd tag, then the point models the command status of the fan:

• false (off) or true (on)
• variable speed then it is 0% (off) to 100% (full speed)

If annotated as an input with the sensor tag, then the point models a sensor used to verify the fan status:

• false indicated no air flow (off) or true indicates successful airflow (fan is on)
• if numeric the point is differential pressure across the fan measured in "inH₂O" or "kPa"

Edit: you actually have two points - one for the command and one for the feedback sensor

I would like to add the fact that for a fan status, if numeric, it could also be a current reading (A). Status On/Off would be calculated with a compare block (same thing as diff.pressure).

Is there a way to differentiate from pressure ?

@Christian - What you've described here is actually 3 different points that would all be modeled differently.

• current point: sensor and current
• fan status point: sensor and fan
• pressure point: sensor and pressure

I think one thing to always keep in mind is that points should always be tagged and modeled as what they really are and not what they are interpreted as. If they can be interpreted different or calculated into something else, then it is another point tagged differently.

@Joe if so, fan tag would need to be modified. I've just referred to the existing fan tag (see Brian post up here)

Good point Christian. If we are associating more than just cmd and sensor points to a fan, then the fan doc needs to change. In my above 3 points I technically only associated the status with the fan. But you could easily make the argument that the current should as well.

• current point: sensor current fan
• fan status: sensor fan
• pressure point: sensor pressure

I've also made the argument in the past that at some point fans and pumps should be considered equip because of the amount of points that can be associated with them. Especially when we get into VFD's, which can have numerous power points and others directly associated with them. I'm not sure if we want to quite make that jump yet...

What if fan status is the result of a calculation ? It's not a sensor....

Could haystack provide tags for calculations/demands (cooling demand, heating demand, etc)/PID output and so on ?

I think this sort of discussion really gets into the fact that a complex VFD might really be its own sub-equipment with many of the same points as you might find in an elecMeter such as current, demand, consumption.

If we do flatten it and stick them all as points on the AHU, then I think we combine the existing elecMeter points with the discharge fan tags.