VXI SVM2608 Resistance Measurement Offset Method, Resistance Measurement Dynamic Method

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Resistance Measurement – Offset Method

The value returned by the resistance measurement offset commands (0x0022 through 0x002D) is calculated using two current values. A voltage is measured when a current (I) is applied to the circuit (VON) as well as when the current is not applied (VOFF). The offset resistance value is then calculated using the following formula:

Offset Resistance Measurement = VON − VOFF

I

This might be useful when trying to measure a resistance in the presence of a voltage.

Resistance Measurement – Dynamic Method

The dynamic measurement resistance commands (0x002E – 0x0039) are used to determine a resistance value for a given current while taking the non-linear nature of the current versus voltage curve produced by diodes. The measurement is performed using two currents. The initial current, I1, produces the initial voltage, V1. A second, lower current, I2, creates a second voltage, V2. The dynamic resistance measurement value is calculated using the following formula:

Dynamic Resistance Measurement = V1 − V2

I1 − I 2

When dynamic resistance is measured in the lowest current range (highest resistance range), no “lower” current value exists. In this instance, current is turned off for the second measurement (I2 = 0). In effect, this measurement is the same as an offset resistance measurement.

Self Test Command

The Perform Self Test (0x0011) command instructs the processor to perform an internal test using the on-board reference voltage and on-board reference resistors. The purpose of this test is to verify the functionality and accuracy of the system. A failure is indicated if the measurement is not within 0.8% of the correct value.

This command can be sent to each channel independently to perform a self test on that channel, the result of the self test is placed at the base offset for each channel (i.e. 0x000000 for Channel 0, 0x200000 for Channel 1, etc.). Each one of the 32 bits indicates the FAILURE (bit = 1) or SUCCESS (bit = 0) of a test as follows:

For Channels 0 – 3:

Bit 0 - Measures +0.945 V on the 1 V scale

Bit 1 - Measures -0.945 V on the 1 V scale

Bit 2 - Measures +0.945 V on the 2 V scale

Bit 3 - Measures -0.945 V on the 2 V scale

Bit 4 - Measures +0.945 V on the 5 V scale

Bit 5 - Measures -0.945 V on the 5 V scale

Bit 6 - Measures +9.45 V on the 10 V scale

Bit 7 - Measures -9.45 V on the 10 V scale

Bit 8 - Measures +9.45 V on the 20 V scale

Bit 9 - Measures -9.45 V on the 20 V scale

Bit 10 - Measures +9.45 V on the 50 V scale

Bit 11 - Measures -9.45 V on the 50 V scale

Bit 12 - Measures 128 Ω on the 100 Ω scale

Bit 13 - Measures 128 Ω on the 1 kΩ scale

SVM2608 Programming

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Contents SVM2608 VXI Technology, Inc Table of Contents Self Test Command Restricted Rights Legend WarrantyLimitation of Warranty CertificationSteve Mauga, QA Manager EMCUse Proper Power Source Service should only be performed by qualified personnelTerms and Symbols Use Proper Power CordImproper Use Avoid Electric ShockGround the Product Operating ConditionsTechnical Support VXI Technology World HeadquartersVXI Technology Cleveland Instrument Division VXI Technology Lake Stevens Instrument DivisionVXI Technology, Inc SVM2608 Preface Overview IntroductionScale Triggering Acquiring DataDelayed Trigger Linear ModePre-Trigger Test Bus Fifo ModeCommands CalibrationsOption SVM2608 Block Diagram Physical Description SVM2608 Environmental SpecificationsCH1I+ GND CH3I+ Exttrigin CH0I CH2I Front Panel Interface WiringGND CH1I CH3I GNDMtbf SVM2608 SpecificationsOption 1 SVM2608-01 VXI Technology, Inc SVM2608 Introduction Setting the Chassis Backplane Jumpers Calculating System Power and Cooling RequirementsRotary Switch Locations Setting the Base AddressDivide Decimal ExampleMSB LSB Module INSTALLATION/REMOVAL Switch to C and the front switch toRegister Offset Device Memory MapsFunction Offset ReservedMS = Most Significant LS = Least Significant SVM2608 A32 Register MAP0x72 Command Register Channel 0x74 Databyte Ordering Determining the Register Address Description of Registers Accessing the RegistersSysfailctl EXT Trig Slope Force Trigger, Start Register 0x02 Read & WriteINTLVL2 HSTRIGSRC2Reserved TimeoutctlExternal Trigger Level 0x06 Read & Write ATTN-GAIN1-GAIN0 2WIREOHMS4WIREOHMS LINEAR/FIFOSample Rate 0x0E, 0x36, 0x5E, 0x86 Read & Write Sample Rate 0x0C, 0x34, 0x5C, 0x84 Read & WriteKHz Channels 0-3/5 MHz Channels 4-5 LPF Control This bit Sample Rate, High-Speed 0xAE, 0xD6 Read & Write Sample Rate, High-Speed 0xAC, 0xD4 Read & WriteTimeout 0x1C, 0x44, 0x6C, 0x94, 0xBC, 0xE4 Read & Write Fifo Data 0x26, 0x4E, 0x76, 0x9E, 0xC6, 0xEE Read Only Fifo Data 0x24, 0x4C, 0x74, 0x9C, 0xC4, 0xEC Read OnlyReserved Registers 0xF8 0xFC Trigger Delay = Measurement Commands Microprocessor CommandsCaptured Data Calculations Resistance Measurement Offset Method Self Test CommandResistance Measurement Dynamic Method Example Preset Setting Measurement CommandsTrigger Event Forced Trigger Calibration CommandsSample Points Sample RatePage Error Processing There are no errors in the queue Diagnostic Commands Changes become effective the next time the module powers up Examples Example 2 Setting Channel 2 to Acquire 200,000 SamplesExample 3 Setting Channel 2 to Pre-acquire 100,000 Samples Timeout Register = Timeout Base * 213 + Timeout Counter Timeout Counter = Timeout / Timeout Base ClockVXI Technology, Inc SVM2608 Programming Data Swapping Example Appendix aVXI Technology, Inc SVM2608 Appendix a Index
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