RS7 testing G.Rutter Ltd 2013

Transcription

1 RS7 testing G.Rutter Ltd 2013

2 Design Overview The RS7 is designed around the powerful PIC16F785 chip which in addition to basic microcontroller (MCU) logic also includes a voltage reference, op-amps, A-D converter & PWM output. All RS7 functions are controlled by this IC. The RS7's functions can be divided into: 1. High voltage generator: this uses a simple oscillator around Q1/L1 charging C1 to a voltage set within the MCU. 2. Output current controller: this uses Q2 as an open collector current sink. The base drive is derived within the MCU using PWM to set the output current and negative feedback via R11 to an op-amp. 3. Output current measurement: via R12/C7 to the A-D converter 4. Battery voltage measurement: internal to the MCU 5. Input keys: to reduce pin count there is some multiplexing. The ToF key resets the MCU in case of a malfunction 6. LEDS and sounder: all are driven directly by the MCU Calibration Calibration of the RS7 is performed semi-automatically through a software routine built in. Calibration can only be performed after programming: once calibrated the parameters are stored in EEPROM for the life of the instrument and the calibration routine cannot be started again without reprogramming. Recalibration should not be required unless major components are changed, and can only be carried out by the manufacturers Parameters calibrated: 1. Voltage measurement relative to the built in voltage reference 2. Output current set at 60mA (other currents pro-rata) 3. Output current measurement (at 60mA, other currents pro-rata) 4. The HT inverter voltage is fixed: this is checked but not calibrated

3 Testing: quick test For a quick test of the RS7 output and basic functions: 1. Use the RS7 with its own (battery) power supply 2. Press up & down keys simultaneously to read battery voltage on LED bargraph: should read at least 3V on left hand scale. If less than 2.8V, replace batteries. 3. Connect a 2,000 ohm resistor across the output using 4mm plugs, and if possible connect an oscilloscope across the resistor (voltage range up to 160V) 4. With current set to default of 60mA, press 'Tet'. Bargraph should read 60mA, and 'scope should show square pulses of 200us, 120V, 50Hz 5. Repeat (4) pressing 'ToF' and 'DBS' 6. Disconnect 2K load and press 'Tet' again. No bargraph LEDs should light up showing no current 7. (Optional) Repeat (4) with other current settings: 40mA, 80mA suggested 8. (Optional) Remove batteries, disconnect from 'scope and connect to a variable PSU to test accuracy of battery voltage indicator and low battery warning

4 Instruments required: 1. Power supply up to 3V, 200mA 2. Voltmeter 3V-300V 3. Current meter max 200mA Testing: full test 4. Oscilloscope, pref. DSO, set to 50us/div, 1V/div 5. Accurate 100R resistor 6. Variable resistor 10K Setup: The RS7 output should be connected to a variable resistive load of 10K in series with 100R, with the +ve output to the 100R and the -ve to the variable 10K. The DSO should be connected across the 100R with its earth connected to the RS7 +ve output. The 100R should be accurately calibrated as it is to be used for measuring the output current. The battery terminals should then be connected to an accurately measured 3V supply of at least 200mA, preferably with integral current monitoring. The output of the RS7 is floating therefore not more than one instrument can be connected to mains earth. This would normally be either the power supply or DSO. Because of capacitive coupling to earth it may not be possible to get accurate waveforms on the DSO unless the PSU is disconnected and batteries used instead. The DSO will show negative pulses. Procedure 1. Set current at 60mA: with 3V supply press the Tet key, observe the output on the DSO and record output current, positive output terminal voltage, and supply current. Varying the load resistance should have little effect on the output current up to about 2K, after which it will reduce. This current measured on the DSO should correspond to that shown on the 8 LED bargraph. 2. Repeat step 1 at other current settings: 80mA, 40mA. At 80mA eight LEDs can be observed to function. 3. Check operation of ToF and DBS key 4. Battery voltage check (press Up/Down keys simultaneously) should show 3V 5. Press and hold DBS to initiate 1 minute repeats. Reduce supply voltage until red 'low batt' LED illuminates (should be approx 2.6V). Reduce voltage further to 2.4V and test operation again (NB output voltage will drop below normal range) 6. Return to 3V supply. Disconnect neg. output terminal, press 'Tet' and measure and record maximum output voltage. 7. Test Lock function (DBS/Tet keys simultaneously) 8. After at least 10 seconds, and with the output disconnected, check supply current <1uA. (NB In normal use the RS7 idles for about 1 hour after use during which time it remembers its current setting. Because of this, unless the RS7 is turned off by either a voltage check or lock, the supply current will remain at 1-5uA for about 1 hour.)

5 Circuit diagram

6 Specifications Power source 2 x AAA alkaline cells battery lifetime >1 year in normal use Low battery warning 2.6 volts ( V) Battery voltage indicator Accurate to 5% Output Output current Maximum voltage Minimum voltage Battery current Battery current Battery current Stimulation pattern: Train of Four (ToF) Double Burst (DBS) Tetany (Tet) Post tetanic count (PTC) square wave pulses 0.20ms ( ms) 10-80mA into 0 to 2500 Ohms accurate to 5% volts (no load) 200 volts (1 Kohm, tetany) <1uA (off) <5uA (paused) <150mA (tetany, 80mA) ToF and DBS can be set to repeat every minute 4 pulses at 2Hz 3 pulses at 50Hz, pause 0.7s, 3 pulses at 50Hz 50Hz for 4 seconds max 1Hz for 20s Manufacturer: G. Rutter Ltd Kaimosi Pyle Hill Woking Surrey GU22 0SR