hv_source.py

#!/usr/bin/env python

import time
import serial

"""
This is the HV object the controls communication between
the computer and the Glassman HV supply.
"""
class HV(object):
    
    default_current_limit = 0.005    # max 5 mA current draw
    
    def __init__(self, port='/dev/tty.usbserial-A4007BoA'):
        self.port = port
        self.start_serial(self.port)

    #Open a port for serial communication. 
    def start_serial(self, port):

        # Configure the serial connections 
        # These are specific to the Glassman HV supply
        self.ser = serial.Serial(
                port=port,
                baudrate=9600,
                parity=serial.PARITY_NONE,
                bytesize=serial.EIGHTBITS,
                stopbits=serial.STOPBITS_ONE)

        time.sleep(.25)
        
    def write(self, command):
        self.ser.write(command)
        time.sleep(.25)  # This delay allows response.
         
    def close_serial(self):
        self.ser.close()

    def read(self):
            out = []
            while self.ser.inWaiting() > 0:
                data = str(self.ser.read())
                out.append(data)
            if out != '':
                return ''.join(out)
            else:
                return None

    def write_and_read(self, command):
        self.write(command)
        return self.read()
        
    def hv_on(self, volts, currentLimit = default_current_limit):
        self.set_voltage_and_current(volts, currentLimit)
            
    def hv_off(self):
        self.set_voltage_and_current(0, 0)
        
    # This turns on the high voltage and sets a current limit
    def set_voltage_and_current(self, volts, currentLimit):
        command = self.build_HV_command(volts, currentLimit, 'on')
        response = self.write_and_read(command)
        if response != 'A \n' and response != 'A\r':
            print("Error from HV supply: "+repr(response))
        
    ################# Command Building Methods ##################    
    
    def build_HV_command(self, volts, currentLimit, power):
        header = '\001'
        identifier = 'S'
        voltage = self.find_voltage_setting(volts)
        current = self.find_current_setting(currentLimit)
        dumbZeros = '000000'
        if power.upper() == 'ON' or power == 2: power = '2'
        if power.upper() == 'OFF' or power == 1: power = '1'
        if power.upper() == 'RESET' or power == 4: power = '4'
        command = identifier+voltage+current+dumbZeros+power
        checksum = self.find_checksum(command)
        return header+command+checksum+'\r'
        
        
    # Returns two character for the checksum of a given command
    def find_checksum(self, command):
        i = 0
        for c in command:
            i += ord(c)
        remainder = i % 256
        checksum = hex(remainder)[2:].upper()
        for i in range(2-len(checksum)): checksum = '0' + checksum
        return checksum
    
    
    # Finds voltage settings given an absolute voltage. 
    # Returns three characters for the voltage command.
    def find_voltage_setting(self, absVoltage):
        if absVoltage > 5000:
            print("Max voltage setting 5kV. Setting to 5kV.")
            absVoltage = 5000
        scaled = int(absVoltage/5000.0*4095)
        command = hex(scaled)[2:].upper()
        for i in range(3-len(command)): command= '0' + command
        return command
        
        
    # Finds current limit settings given an absolute current. 
    # Returns three characters for the current command.
    def find_current_setting(self, absCurrent):
        if absCurrent > 20E-3:
            print("Max current setting 20mA. Setting to 20mA.")
            absCurrent = 20E-3
        scaled = int(absCurrent/20E-3*4095)
        command = hex(scaled)[2:].upper()
        for i in range(3-len(command)): command= '0' + command
        return command
        
    ################# Response Reading Methods ##################  
    
    # Ask the Glassman to tell us its status
    def get_status(self):
        # Build the query command
        header = '\001'
        identifier = 'Q'
        checksum = '51'
        command = header+identifier+checksum+'\r'
        # Send query and return response
        return self.write_and_read(command)
        
    def get_voltage(self):
        status = self.get_status()
        # Analog monitors have 10-bit resolution, max = 3FF = 1024
        scaled_voltage = int(status[1:4], 16)
        return scaled_voltage/1023.0*5E3
    
    def get_current(self):
        status = self.get_status()
        # Analog monitors have 10-bit resolution, max = 3FF = 1024
        scaled_current = int(status[4:7], 16)
        return scaled_current/1023.0*20E-3
        
    def get_voltage_and_current(self):
        status = self.get_status()
        # Analog monitors have 10-bit resolution, max = 3FF = 1024
        scaled_voltage = int(status[1:4], 16)
        scaled_current = int(status[4:7], 16)
        return scaled_voltage/1023.0*5E3, scaled_current/1023.0*20E-3
        
    def check_ready(self):
        status = self.get_status()
        # Very basic test, just want to hear something
        if status == '':
            return False
        else:
            return True