7 Attachment(s)
DC temperature/pressure meter
This thread is about a recently home made Digital Dust Collector Pressure/Temperature meter.
The first post will be a general description of meter. Subsequent posts will provide additional detail of some of the technical detail such as design, build, testing and calibration and use .
The story is I’m still feeling too knackered to be standing at the bench in the shed for more than about half an hour before I need a rest, plus it's been a tad hot so I decided to retreat to the house and work on some electronics projects. This is a project I have been meaning to tackle for some time but it’s taken me a while to get all the pieces together.
The temperature being measured is the temperature of the 3 phase, 4HP, DC impeller motor - DC located in an enclosure outside my shed. The motor runs on a 240V VFD and although the VFD has current limits set , it does draw quite a high current at higher speeds so I would like to know the temperature of the motor. Whatever it is, it should be considered in relation to the temperature of the air inside the DC enclosure so the meter provides that information as well.
The Pressure reading output depends what the sensor hose is hooked up to.
Usually it will be the pressure (relative to atmosphere)in between the impeller and the DC filters, as this can be used as a measure of when the filters need cleaning.
Attachment 449157
What's inside the box.
Attachment 449160
The unit is based on an Ardunio “Zero” micro controller (MC). Labelled "A" in the photo above.
The black rotary switch (#data points in photo) sets the number of readings averaged before displaying data. This can be 1, 2, 5, 10, 20, 40, 60, 80 or 99 readings.
The DST data switch toggles the screen display between P/T data, and the raw digital data output (numbers would always between 0 and 4095) by the MC.
Reset (R) - resets the MC.
The temperature sensors are K type thermocouples (TCs) are located in the DC enclosure and require a small operation amplifier (OA in photo) to boost the small microvolt signals into the sensing range of the MC.
The pressure sensor (P orange arrow) is located inside the MC box as it is sensitive (see subsequent posts about this) and can measure pressure differences of ~0.01 inches (0.25mm) of water column (or 0.0025 kPa).
A small daughter board is used for the OA and P and for additional ground, 3.3V & 5V supply points . P is underneath the daughter board.
Attachment 449164
Referring to 2 photos back, brass flange (F) connect the pressure sensor to an outlet (P in photo below) outside the box suited to 4 mm diameter black HSPE trickle irrigation tubing which is used between the MC box to hook up and measure up any required pressure measuring points/holes in/on the DC system.
Attachment 449162
Plug and socket (T) connects via an ~ 3 m long cable to the temperature sensors in the enclosure .
The connections are housed in the small black plastic boxes (M & E) shown below.
The thermocouples (temperature sensors) are the fine brown and yellow insulated wires coming out of the plastic boxes - these will be tucked away under something thermally conductive like a small Al block.
Attachment 449163
The Motor Temp thermocouple (Motor T) is embedded inside an Aluminium block attached to the cast iron motor housing inside the motor power junction box.
The other (Enclosure T sensor) just hangs from the ceiling of the DC enclosure
Display.
The P/T data display page is pretty self explanatory
Motor T is the motor temperature
Enclosure T is the enclosure temperature
Diff is the the between the two measured temperatures.
DCP is the pressure relative to atmosphere in kPa of whatever the pressure sensor is connected to .
The number "9" on the bottom right of the screen is a count down number and shows the current data point being displayed.
This also tells the operator where it is in the data collection cycle.
Data is accumulated from every sensor at a rate of about 100 points per minute.
Attachment 449161
The 12 Bit ADC Raw data display is a diagnostic display screen and is the output of the analog sensor ports (S1 =enclosure, and S2= motor) these should always be between Amax (a constant 4095) and Amin (should be zero but there is always an offset)
AP is the digital output of the analog port the pressure sensor is connected to.
The 12 Bit ADC Raw data is also used to calibrate the sensors.
Attachment 449168
Clear as mud?
Further details are provided in subsequent posts.