1 2 3 1.0 INTRODUCTION 1.1 Description of the Equipment The model 615 ARM (Anhysteretic Remanent Magnetization) system is designed to enable magnetization of rock samples during demagnetization with the model 600 Degaussing System. The rock magnetization is achieved by applying a dc magnetic field in the range 0 to ±4 Gauss during the degaussing process. The model 615 system is capable of energizing two coils, typically an axial solenoid and a transverse Helmholtz pair. The field application coils are mounted to the degaussing coils of the model 600 Degaussing System. In the case of the transverse Helmholtz pair, the field application coils are mounted to the inside face of the model 601T Transverse Degaussing Coils. For axial discrete sample samples, the field application coil consists of a solenoid mounted inside the model 601 Axial Degaussing Coil. For long core systems, the field application coil consists of a long solenoid extending through the axial degaussing coil from one end of the degausser mu metal shield to the other. This long solenoid ensures that a steady dc field is applied to the long core on either side of the degaussing coil where the AC field is decaying to zero. The ARM electronic system consists of a constant current source which enables the creation and maintenance of a dc magnetic field even when the large back EMF created by the degaussing coils is present. The magnetic field can be set either manually or optionally by computer command if the system is equipped with a single board computer interface option. In either case, actual magnetic field present is shown on a front panel display. 1.2 Front and Rear Panel Description The front and rear panels of the model 615 ARM system are shown in Figs. 1 and 2. Power The front panel power switch turns on system power from the mains. An indicator light located just above the power switch illuminates when the power is on. Direction This switch controls which of the two ARM coils is to be energized. The LEDs denoted "axial" and "transverse" denote the active coil. Operation This switch selects between manual or computer operation. Appropriate LEDs illuminate to indicate the selected mode. Field Adjust This front panel potentiometer enables magnetic field magnitude adjustment when the system is in the manual mode. This pot is not active when the computer mode is selected. 4 fig 1 5 fig 2 6 Field This display indicates the magnitude of the magnetic field in Gauss. Voltage This display indicates the voltage required to produce the displayed field value. Mains Power Input Connector This rear panel connector is used to connect power cable to the system. The connector assembly enables the input voltage selection of either 115v or 230v. CAUTION !! Ensure that this voltage selector is in the "correct" position before applying power to the system. The power input connector also houses a power fuse. This can be removed for inspection by using a small screwdriver to pry the fuse holder insert out of the power connector panel. Axial and Transverse Connectors These connectors enable connection to the magnetization coils mounted inside the degausser shield assembly. Computer This connector is a serial COM port connector which enables connection of the system to an external computer. 1.2. System Specifications Field Application range 0 to ±4 Gauss Field Uniformity over sample volume discrete sample 5% long core (inside solenoid) 2% Field Accuracy ±2% Constant current compliance voltage 80v peak to peak Size of control chassis 19" x 5" x 12" Weight of control chassis 10 lbs. Power 115v @ 1 A 230v @ 1/2 A 7 2.0 OPERATION OF THE EQUIPMENT 2.1 Initial Setup The system consists of a control console, one or two field application coils and interconnect cables. After unpacking the system, connect a power cable to the rear of the control console. Check to make sure that the voltage selector switch is properly set between 115v and 230v for the local power. Normally the field application coils will already be mounted to the degaussing system coils. Connection to each field coil is made by using a 2 conductor cable. Connect these cables to the rear panel control console banana plugs. These cables should be connected at the field coil end to screw terminals mounted on the degausser coils. Long core axial solenoids normally have leads permanently connected to the coil and hence only need to be connected to the ARM control console. 2.2 General Performance Check After setting up the ARM system, turn on the system power. Choose manual operation and select an appropriate coil. Now adjust the field setting potentiometer to create a convenient field value (i.e. 1 Gauss). Note as you increase the field amplitude, the coil voltage also increases as indicated on the front panel field amplitude display. If you have a fluxgate magnetometer, you can check the accuracy of the field setting by placing the magnetometer in the middle of the field application coil. CAUTION !! When measuring fields inside degaussing coils, make sure they are not energized. A good precaution to take is to turn off the degausser power amplifier. Degaussing coils with very high and potentially lethal voltages are energized during operation. After setting the ARM field magnitude, a degaussing sequence can take place. This will result in the imparting of a permanent magnetization to the specimen during degaussing. CAUTION !! The cables which connect the ARM coil to the ARM control console enter into the high voltage degaussing region. These cables are isolated from the degaussing coils and are safe to handle even when energizing the degaussing coils. However, it is good practice to avoid touching these cables during degaussing and, in addition, they should be routed so that they are out of the way. 8 3.0 THEORY OF OPERATION The ARM electronics consist basically of a constant current source capable of applying a maximum of 4 amps output; this current can be maintained even in the presence of a back AC emf of up to 80 volts peak to peak created by operation of the degaussing coil. The circuitry of the ARM system is divided into two p.c. boards. The circuit diagrams for these two boards are shown in Figs. 3 and 4. The circuits shown in Fig. 3 comprise the high voltage compliance constant current source. IC U2 provides up to 4 amps of current over an input voltage of ±40 volts. Current is sensed by monitoring the voltage across R8. Any AC voltage due to back EMF is detected across this resistor and a canceling voltage is developed and fed back to U2 via buffer IC U3. The main field setting is done by adjusting a potentiometer connected to JP1. Switching between the 2 possible ARM coils is accomplished by a front panel switch connected to JP3; this switch is used to activate relay K1 which switches between the coils which are connected to JP4. Fig. 4 shows the support ARM electronics consisting of ±15 and +5 volt power supplies shown in the upper left of Fig. 4. A reference circuit consisting of U1 and U2 produce ±5 volt references for energizing the field setting potentiometer. Connection to a single board computer is accomplished by using ribbon cable connector JP15. Connection between the power supply p.c. board is accomplished by using JP15. Potentiometers R6 and R7 enable the calibration of the front panel field display directly in Gauss. Front panel switches are connected to the p.c. board by means of P16. IC U5 provides a de-bounce function for these switches. Connection to the two front panel displays is achieved by means of JP11 (field readout) and JP12 (voltage readout). Logic to control LEDs is provided by U4. The LED drive current is sourced by the driver U7. 9 4.0 Computer Interface The ARM is equipped with an RS232 computer interface that allows field and axis control of the unit. Status information can also be obtained from the ARM as well. The computer connection to the ARM unit is via a DB25 female connector on the back panel. The protocol used to communicate with it is as follows: baud rate -- 1200; dataword -- 8 bit; parity -- none and stop bit -- one. No handshaking protocol is used. The commands are as follows: Send ARMSS (ARM Send Status) Response M X A X S X F X X X X M = Mode X = “M” or “C”; C = Computer mode, M = Manual mode A = Axis X = “A” or “T”; A = Axial, T = Transverse S = Status X = “N” or “O”; N = Normal; O = Overrange Note: If the unit becomes overranged, it will send back an uppercase message “OVERRANGE” F = Field Setting in Gauss The limits on the field are ±10.00 Gauss. Example: A field of 5.00 Gauss will come back as 500 To configure the ARM, enter the command: ARMCX the “X” is replaced as follows: To configure Axis, enter the command: ARMCAX X = A for Axial or X = T for Transverse 10 To configure Field, enter the command: ARMCF XXXX where X = value Example: to set field to 5.00 Gauss, enter the command: ARMCF 0500 To set field to -10.00 Gauss, enter the command: ARMCF - 1000 Gauss Note: Not all ARMs will be able to reach a maximum field ±10 Gauss. The maximum field will depend upon the type of ARM coil used. .