Municipal Water Meter Monitor
IntroductionFor years I have been able to monitor the power usage of the home with the Power Node. One project I have been meaning to tackle is to monitor the water usage as well. The photo below shows my main water meter. I also have a "sub-meter", which measures the water usage in the garden. I do not pay for sewer charges for water used by this latter meter, saving me a lot of money during the growing season.
Photo of the front dial of the main water meter. It is a "Model 25L" with a Thermoplastic body
per the company web site. Note the copper wire seal near the bottom left of the picture.
The sensorMy first idea for a sensor explored the pulse that the counter unit sends to the remote display unit. Unfortunately, one pulse is sent for every 100 Gallons, and this is much too low a resolution for my use. My second idea was to pick up the small white arrow on the water indicator dial (marked "10 Gallons" on the front dial) using an optical reflective sensor. Since this indicator makes one revolution per 10 Gallons, I decided to use four phototransistors arranged in a circle to increase the resolution to 2.5 Gallons.
I built the LED and phototransistor circuit and mounted it onto a small piece of perforated printed circuit board and a solderless breadboard. In actual tests I found that it was very difficult to pick up the small white arrow. I was concerned with the difficulty in aligning the sensor over the dial's window, and drift with voltage and temperature. After a few days of optimizing parameters such as component values and sensor placement, I gave up on this idea.
My third idea exploits the fact that water usage information is transferred magnetically from the collection unit to the counter unit. This means that the flow of water causes a spinning magnetic field. I wondered if I could pick up water flow information by sensing this magnetic field. My initial tests with a simple magnetic field sensor -- a compass -- proved promising. As water flows, the compass needle flickered at a rate proportional to water flow.
Hall-effect sensor with the wiring attached.
Calibration and useWhile filling a container, I observed the number of counts detected from the sensor. I measured 100 counts per gallon, and since this is a nice round number, I presumed that the designers' intended for 0.01 gallons per revolution of the drive magnet. Being able to measure the water usage down to the nearest one hundredth of a gallon is quite amazing to me, as this is much higher resolution than I need. Since this is essentially a digital measurement, the reliability is very high. The software on the power node was updated to keep track of the number of pulses on this sensor, and the accumulated byte is sent to the Home Control Program when queried. A 32 bit quantity is used in the program to track this byte's rollover. As long as the byte does not roll over between polls of the counter, no water usage will be lost. In the current configuration, the system can handle any water flow rate that is less than about 150 gallons per second.
With suitable software, it is even possible to double the 0.01 gallon resolution by counting not just the rising edges of the Hall-effect sensor, but also the falling edges. Thus it is possible to measure the water use of the home to almost within a tablespoon (15ml).
As with all other data collected by the Home Control Program, water use can be plotted over the course
of one day. Here, the water usage in gallons is shown (in yellow) along with the powerline voltage (red),
and the power usage in KWatts (green). As the user pauses the mouse over the graph, the corresponding value
is shown with a thin black line and the time below. Thus at 2:40pm, the Total Power was 0.4KWatt, and
the power line voltage was 120.0 Volts. By then, we had consumed 79.5 Gallons since midnight.
CostNot counting the phototransistor-based attempt, the total cost was very low. Just a few dollars for plugs and jacks to allow easy disconnection of the added hardware to the Power Node.
Neptune. To my dismay, the above sensor no longer worked. The weaker magnetic field was confirmed with a compass. Based on the amount of angular deflection of the compass needle (~10 degrees), and the estimated field strength of the earth (~0.5 Gauss), I estimated that a sensitivity in the range of 0.1 Gauss would be needed (I do not recall the field strength of the old water meter).
allows me a price break for water used in the garden. The brown wire leads to
an object on the outside of my home that allows the meter to be read electronically.
Looking on the Internet, I found just the kind of device that I was looking for: an analog field strength meter that was sensitive enough to detect the earth's magnetic field. This unit is the MG-BTA from Vernier Software and Technology. It costs a reasonable $52, and had a simple analog interface. Other analog sensors with displays were about $600.
Image from Vernier's web site on the magnetic sensor.
The sensor is on the end of a probe, which makes
it convenient to locate next to the water meter.
Output voltage of the sensor when held near the Neptune water meter.
- Yellow - 10V out (unused).
- Black - Ground.
- Green - Vres (unused).
- Brown - Identifier (unused).
- Orange - 5V supply (only 10mA current required).
- Red - Sensor Output.
Circuit that converts the analog output to digital pulses for reading by the Power Node.
Test setup for the above circuit in my basement. Note the old sensor on the coil of wire to the right.
The finished project. Note that the sensor is conveniently packaged on the end
of a rod, which allows it to be held as close as possible to the meter. The strongest magnetic field will be right at the interface between the water turbine part (bottom
brass part), and the meter dials (top black part).
In October 2009, Bryan Mumford, whom I assisted in building his own sensor setup, sent me some information on his sensor. By opening up his unit, he found that the sensor chip is the Sentron CSA-1VG.
Screen snap of the web page for the sensor chip
that is used in the field strength meter.
- BadgerMeter, Inc Website for old water meter (Model 25L).
- Hall effect sensors from Digi-Key. Select the 3-pin SIP package for the smallest model.
- New water meter website by Neptune (Model 3/4" T-10).
- Magnetic field sensor from Vernier.
sensor used in the field strength meter.
Long term update/Project Log
- July 27, 2003 - Sensor installed and home control software updated to display water usage. A future update to the program will be an alert if water is wasted (overnight water usage is a slow trickle, or if irrigation is accidentally left on).
- October 12, 2003 - During our Disney World trip, we totalled less than 0.01 Gallons over the course of at least four days. This shows there were no leaks system wide for that duration.
- June 25, 2004 - During our Story Land trip, a
trickle of water at about 1.75 Gal/hr was noticed from the e-mailed
logs from the home. An investigation shows a leaky toilet flapper
in the basement bathroom. After repair, the trickle
stopped. This gives me an idea of how to implement an automatic
monitor (see below).
- August 1, 2004 - Added a new software functionality to the Home Control Program. At the top of each hour, the average water usage rate is calculated. Over the course of one day, the maximum and minimum value for the rate is tracked. When the user moves the mouse over the display of water total on the GUI, a hint pops up with the current hourly max and min rates. In addition, the water display goes red to indicate a problem (see below), if any of the following occurs:
- If the minimum water usage per hour is above 0.2 gal/hr.
- If the total water used exceeds 2000 gals in one day (normal usage with irrigation is no more than ~1500 gallons/day).
- If the total water used exceeds 400 gallons and the irrigation
Example of the Home Control Display if a water
leak is suspected. Current water use to this hour is 14.0 Gallons, but
the minimum flow rate was higher than expected.
- September 9, 2004. Dishwasher (Whirlpool) uses 9.1 Gallons of water per load. This takes less water than handwashing a whole load.
- May 13, 2004. Both water meters changed to Neptune units.
- May 21, 2004. Conversion from Hall-effect sensor to analog magnetic sensor.
- Oct 15, 2009. Added note from Bryan