Design of a High Speed Isolated Signal Transmitter, ST100
This project is for the design of a high speed isolated signal transmitter, called the ST100. It accepts an input voltage or current signal, electrically isolates it, conditions it and outputs the resulting signal. Isolation is needed to protect the equipment reading the output signal from high voltages on the input side. Signal conditioning includes an adjustable gain and offset. The ST100 can transmit signals up to 10 kHz which is significantly faster than similar product currently on the market which can only transmit up to 10 Hz.
Over 200 of Alaska’s communities generate their own electricity in remote diesel microgrids. The high cost and unreliable supply of fuel to these communities is indicative of the challenges faced worldwide by remote microgrids, a rapidly growing market. The Alaska Center for Energy and Power (ACEP) focuses on reducing energy costs in remote microgrids though the reduction of diesel consumption, often with renewable energy. Powering a small grid with variable energy resources such as wind and solar is challenging due to the fast changes in available power production and the load. In order to respond to these fluctuations, the grid needs to be able to make fast electrical measurements. In order to run simulations of these microgrids, data measured at a high frequency is required to capture all the dynamics. ACEP has been developing measurement systems that can measure at a 1 kHz sample rate. However, all isolated signal transmitters on the market (necessary to isolate the measurement equipment from voltage spikes on the measurement line) are only capable of measurements of several Hz. Because of this, ACEP has developed a high-speed isolated electrical signal transmitter called the ST100. This product can transmit current and voltage signals with frequencies up to 10 kHz while providing 5 kV of isolation between the measurement line and the measurement equipment. This represents a significant improvement over products currently available on the market, is crucial to ACEP’s work and fills a hole in the market.
The ST100 is a high-speed signal transmitter. A signal transmitter has an input and an output. The electrical signal that needs to be measured is fed into the input, the transmitter isolates it, conditions it, and sends the resulting signal to the output. The output is connected to the measurement system (data acquisition or control system) which stores the value or uses it to make a control decision.
An example application of the ST100 is shown in Figure 1. A sensor converts the high voltage or current on a power line to a low voltage or current. The output of the sensor is susceptible to high voltage and current spikes. The ST100 isolates and conditions the output so that it can be safely read by the measurement system.
Signal isolation means there is no electrical connection between the input and output signal. This is essential to providing protection for expensive measurement systems from high voltage and current spikes. Signal conditioning allows the user to adjust the output signal to match the voltage range of the measurement system. It can be adjusted through a push button and LED interface.
A signal transmitter must be fast, safe and accurate. The ST100 uses a novel design that allows it to transmit signals up to 10 kHz, provide 5 kV of isolation, and is accurate to within 0.2% of the input signal. These are significant improvements over the representative current industry standard Acromag 611T which transmits signals up to 3 Hz, provides 1 kV of isolation and is accurate to within 0.5% of the input signal.
Next steps in the development of the ST100 include some further testing, refining into a marketable product, obtaining an UL safety listing and finding partners willing to help bring the ST100 to market.
Left Figure: Sample application of the ST100.
Middle Photo: The ST100.
Right Photo: Adjusting the gain and offset on the ST100.