Things that Work! Remote Measurement Systems ADC-1 Chris Greacen What is a battery's voltage profile over a number of charge/ discharge cycles? When it's added up, does most of the wind turbine's output come from constant breezes, or the gusts? Do the clouds which arrive in the afternoon mean the photovoltaic panels should face east of south? How much more energy does a tracked module put out, month by month? How do we use power in the course of the day? Answers to these questions require loads of measurements, taken at constant intervals, for long periods of time. You could dedicate your days, and those of a few friends, recording measurements like clockwork, armed with a multimeters, clipboards, and superhuman patience. Indeed, this is the way we've collected data for dozens of tests on inverters, charge controllers, and pv modules in past issues. This is a job for a machine Ä a data logger Ä a sort of a super multimeter which records measurements from different sensors into a computer at constant intervals. Here at Home Power we lusted after a data logger for over a year. We looked at units by big companies like Fluke and Hewlett Packard, but found these machines built with too many features (high speed, internal microprocessors and data storage) driving the price up into thousands of dollars. Often the machines were designed for companies like Boeing, who want to take 10,000 measurements a second on jet engines. We don't need that Ä we need to take measurements once every few minutes, or every few seconds at most. Besides, none of these machines interfaced gracefully with the Macintosh computer. Imagine our delight when we received, to test, the Remote Measurement Systems ADC-1. It's a 12 bit resolution, ñ0.1 mV accuracy data logger, and the bare bones units sells for $489. With some added hardware for appliance control, a power supply and serial cable, and software to run on the Macintosh, it is packaged as the "EnviroMac", and sells for $899. The ADC-1's 8" x 7" x 12" blue aluminum box has four terminal strips on the front for 16 differential analog inputs, 5 digital inputs, and six controlled outputs. Inside the box, analog to digital (A/D) circuits change the voltages you want to measure into a digital signal for the computer. This signal travels through a RS-232 connector into the computer (on the Mac, it plugs into the modem port). The ADC-1 is powered by a 9 volt, ac adaptor. It can run on as little as 20 mA at 5 Volts. A cable from the ADC-1 also runs to a "BSR" ac line-carrier remote control system. This plugs into an ac outlet and allows the computer to send signals over your house ac lines to control up to 32 appliances plugged into BSR modules (you get one module in the EnviroMac package). The ADC-1 also has six controlled 5-Volt TTL outputs. This means it's not just a data- acquisition system Ä your computer can make decisions based on the data, and turn on and off appliances. For example, you could program your computer to control heating, cooling and airflow in your home, water your garden depending on soil moisture, and work as a security system. For Macintosh Users On the second page of the manual it says, "If it takes you longer than 30 minutes [to get the ADC-1 up and running on your Macintosh], then you should call RMS (ask for Keith), and explain what aspects were confusing or time-consuming." Keith is the president of the small Seattle company. I found I didn't need to call Keith. The Macintosh ADControl program is fairly intuitive and user friendly, with buttons and pull down menus. It will run on any Macintosh with one megabyte of RAM. The program allows you to condition the data as it is being created: for example a voltage drop across a shunt could be divided by resistance of the shunt to display current. Stock equations handle inputs like wind direction and speed, or temperature from a variety of sensors. You can build your own 8th order polynomial equations if you like. The software allows you to turn on and off the outputs with IF...THEN...ELSE... statements. For example, I could set it to turn on a fan if the temperature in the living room is greater than in the bedroom, during the hours 10 pm to 9 am. There's three ways to view the data within ADControl. You can watch all the values of inputs and outputs on a formatted two column list. Or you can watch the numerical values of the inputs and outputs superimposed wherever you want on a PICT graphic (we might paste them on picture diagram of our renewable energy system). The third option is a plot of a running line graph of one input. I enjoyed watching this plot form mountains and valleys while monitoring a photovoltaic (pv) array in intermittent sunshine. Excel Data Files In the past, after we'd taken lots of measurements, we'd take our clipboards and enter the data into a Microsoft Excel spreadsheet. From here we'd massage the data, finding averages, sums, products, minimums & maximums, and make the charts and graphs you see in Home Power. The ADControl software will write the data it collects to a file which can be read by Excel, and it does this in the background, under System 7. This means that while we're taking data, we can use the Macintosh for other things like word processing. You can choose which analog and digital inputs to record, how often to sample data (from hours to once a second or so), and whether to put time/date stamps onto each data point. The program will even start a new file for you at midnight if you want. The graph above shows how much current each of our pv arrays contributed during four hours on the 5th of February. Data was sampled every 10 seconds. As I waited while our 25 MHz Macintosh choked graphing these thousands of data points, the words, "invitation to excess" rang in my mind. You want fine grained data? Be careful, you'll get what you ask for. Documentation The EnviroMac unit arrived with over 400 pages of well- written documentation. The Macintosh ADControl software comes with a 170 page manual, but I've found the software intuitive enough that I rarely need to turn to it. The 250+ page ADC-1 manual covers everything else: computer programming, installing and calibrating sensors, turning on and off wireless ac appliance control modules, trouble shooting, and gory technical details on the chips used and modifications you can make. There's a list of far-out current applications for the ADC-1, like monitoring environmental quality for molting blue crabs, or automating a cosmetics manufacturing line. For Other Computer Users If you're an IBM user, you can get the Applications Toolkit for MS-DOS which has demonstrations and example data acquisition programs in BASIC, C, and Pascal. We didn't test it. The 200+ page ADC-1 manual assumes a familiarity with BASIC computer programming, and takes you from the ground floor up in getting an IBM and the ADC-1 to talk to each other. For other older computers, the manual has an appendix of software routines, written in BASIC to read data from the ADC-1. Also included are RS-232 pinouts so you can make your own cables for these computers. The intention is clear: to provide enough info that you can put your dusty old 8-bit computer back to work as a cheap but accurate data logger or controller. Installation We wired the ADC-1 to the Ananda Power panel in our battery room. Inside the Ananda are current sensing shunts (pv current for four arrays, total array current, wind turbine current, DC loads, and current out for different inverters), and points for measuring voltage in our system. Bringing this information to the ADC requires wire which are shielded against electromagnetic fields. The job required 40 feet of high quality information cable salvaged from a television transmitting station. This cable contains 14 shielded pairs. Each pair is wrapped in an aluminum sheath with a bare, uninsulated shield wire. We connected all shields to system ground, and to the GND terminal on the ADC-1. The ADC-1 is limited to analog inputs of ñ400 mV. To measure system voltage, wind turbine voltage, and pv array voltage, we built voltage dividers each with a precision trimming potentiometer. The rest was easy: plug in the power and plug the ADC-1 into the Mac's Modem port. It now lives on the wall next to our main computer. Testing We measured accuracy against a Fluke 87 multimeter on all 16 channels, and the unit was within the 0.1 mV accuracy specified by RMS. The ADControl software works as advertised. We hooked up the BSR ac appliance module. These unit worked, controlling lights via software, but only when our house was powered by a sine wave inverter. When we ran on a PowerStar modified sine wave inverter, the unit failed to respond. We also found the unit did not work with when the appliance was four lengths of extension cord wiring away from the ADC-1 BSR controller. Neither of these failures are surprising: the BSR works by putting a small signal on the ac lines when the ac voltage crosses zero. This signal gets drowned out in funky wiring, and by the jolting switching of modified sine wave inverters. Final Comments There are sensors available for nearly anything you could think of. The ADC-1 is available in versions with instrumentation amplifiers for measuring small signals, in a version with 12 controlled outputs instead of 6, and in a version with 32 single ended analog inputs instead of 16 differential inputs. This is a powerful tool, and it easier to use than we could have hoped. It gives us new fine-grained data on our immediate environment. It gives us the software/hardware link to control systems which live in and shape this environment. It is a way to watch the mosaic of energy flow which is inherent in renewable energy powered homes. You'll be seeing data collected with this instrument in future issues of Home Power. We're impressed. We've going to get two more. Access: Author: Chris Greacen, Home Power Magazine, POB 520, Ashland, OR 97520 ù 916-475-3179 Remote Measurement Systems, Inc., 2633 Eastlake Ave. E., Suite 200, Seattle, WA 98102 ù 206-328-2255 FAX 206-328-1787