Hardware

The following figure shows a block diagram of CMM_III and its external connections:

General setup:

• CMM_III needs 5…24V power supply on PWR/GND_Ext
• The CMM_III Current Path is integrated in series to the DUT, whose current should be monitored.

The measurement values can be read out by the following:

• Digital output via a 32-bit SPI word at LVDS voltage level.
• CAN (High-Speed-CAN with 250…1000 Kbit/s)
• RS232 as ASCII-String via the service interface

Additional features are:

• The RS232 service interface may be also used to configure the module.
• Permanent parameter storage of the configuration in Flash memory
• Calculation of mean, min and max values.
• Current path is electrically isolated from electronics supply and digital IO (up to 150V)
• Detection of reverse current
• Front panel LEDs for power good indication (as of hardware revision 2.0)

1.1Connector Pinning

1.1.1System connector

1.1.2RS232 service connector

Note, that the RS232 is a service connection. Normal operation uses the system connector with CAN or LVDS-SPI interface.

1.1.3Mating system connector

The following components may be used for the mating connector on the test system. 1 connector with 8 high current pins is needed. Different versions for crimping or soldering from two manufacturers can be found in the following table.

1.2Dimensions

CMM_III is designed on a 160mm x 100mm Euro card, including front cover with a width of 25,4mm (5HP) and a standard DIN41612 connector. With these dimensions it fits to standard 19” / 3HU carriers and racks.

1.3Technical data

1.3.1Current Path

Depending on the applied currents, the measurement current path must be wired with a low resistance to maintain low voltage drops. I.e., use short wires and as much high-current-pins as possible – both for current input and current output.

Every High-Current pin may carry up to 40A DC maximum. But more used high current pins with wires of high diameter both yield lower voltage drops and temperature at CMM_III, because of heat conduction. Lower temperature also means lower drift.

1.3.2Current Sampling

1.3.3Module Supply

Apply a power source on PWR_Ext/GND_Ext. It is recommended not to use the DUT power supply to make sure that measurement device power is separate from DUT power. Typical applications use 5V, 12V or 24V power supplies. Several other components may be supplied by the same power source.

Nonetheless, because of CMM_III wide input voltage range, it is possible to use DUT-Power for powering CMM_III.

Note, that current path is disconnected, when no power is applied.

1.3.4DC Accuracy

Accuracy of the module is verified at DC currents. Every module passes a calibration procedure at IRS. The module may be re-calibrated.

1.3.5DC Voltage Drop

Voltage drop is the voltage between current input and output, measured on the module connector. The drop on the female power connector pins and the wiring must be added.

1.3.6On/Off Interface

The digital input On/Off is used to switch the current path of the CMM_III on or off.

The current path is connected, when a high level is applied.

The current path is open, when a low level is applied.

1.3.7CAN Interface

The integrated CAN interface is a common High-Speed CAN interface.

For further details, see datasheet SN65HVD230 and CAN.

1.3.8LVDS-SPI Interface

For further details, see datasheet DS90LV049 and LVDS-SPI.

1.4System Integration

The following section handles the hardware issues about the interfaces for accessing measurement data. For integration of the current path and the power supply, see the remarks in the technical data.

1.4.1CAN

The High-speed CAN interface may be used to read measurement data.

Any High-Speed CAN interface from any vendor may be applied as counterpart for data acquisition. Make sure that termination of the entire bus is implemented properly with two times 120 Ohm at the respective far end of the bus. No other termination resistors are included.

Wires must be twisted pair with an impedance of 120 Ohm.

Every CMM on the bus should run at the same baud rate and use different CAN IDs. CAN ID and baud rate may be configured via the RS232 service interface and are stored permanently in Flash memory.

For integration as a single module in a test system setup, please add a CAN counterpart with a termination resistor of 120 Ohm. CMM_III includes 120 Ohm -termination which can be enabled or disabled by a jumper switch (see figure 3).

If several CMM_III are connected in parallel to one CAN interface, the termination resistor of every single CMM_III has to be disabled. A single termination must be included at the far end of the CAN bus.

See the following figure for disabling of the termination resistor with the jumper switch J3, which is marked in red:

See also CAN Backplane, when using backplane and CAN interface.

1.4.2LVDS-SPI

Implementation Options

LVDS-SPI is integrated to read data from CMM at a higher data rate, than available via CAN. But LVDS SPI may not be used in a harsh test system environment.

For a single module, the following setup may be used. Note, that every signal in the diagram is actually a differential pair. With this setup data rates of approximately 1,5Mbit/s can be achieved. With this speed a sample rate of up to 20kS/s can be achieved for a single module.

When higher data rates than 1,5Mbit/s are applied, the enable and clock line must be fed back to the data acquisition system. With this setup, Data, clock-feedback and enable-feedback may be evaluated synchronously. Otherwise, the delay through the CMM may cause corrupt data.

The LVDS-SPI interface is designed in a way to concatenate several CMM’s in a daisy chain type, as illustrated in the following figure.

The maximum number of CMMs depends on data rate, sampling rate and performance of the data acquisition system. Typical setups are as follows:

Typical setup 1:

• 1…10 CMMs
• sampling rate of 2,5kS/s.
• clock rate of 1,25Mbit/s
• feedback of clock and enable not necessary

Typical setup 2:

• 1…10 CMMs
• Sampling rate of 20kS/s
• clock rate of 10Mbit/s
• Feedback of clock and enable necessary.

Please note, that in any case, the wires for clock, enable, Rx and Tx must be at least properly twisted with a maximum length of approx. 1m. When higher distances must be covered, please use the backplane, described in Backplane for easy connection, including shielded CAT5…CAT7 cables. In harsh environments, always use the backplane.

Data Acquisition with IRS MesSy

The standard device for data acquisition is the IRS MesSy. MesSy is a generic re-usable multifunction measurement device, especially designed for lifetime test of automotive control units.

All software components are integrated ready to use a single CMM or several CMMs in daisy-chain. Evaluation of minimum, maximum and average is included. Streaming of CMM data is available.

For further information see

https://www.irs.systems/id/irs-messy/

https://www.irs.systems/de/id/irs-messy/ (German)

The following table shows the connections of MesSy and CMM:

Following example shows the connection of the communication lines, power and On/Off-control of two CMMs:

Data Acquisition with NI Compact RIO

For data acquisition IRS provides interface modules for the Compact-RIO platform from National Instruments. The software may be integrated into the user’s application. For data acquisition with Compact-RIO please contact IRS.

Custom Data Acquisition

Any module with an SPI-interface may be used for data acquisition, like microcontroller devices. The level of each signal must meet the LVDS standard to maintain proper communication over long wires in harsh environments.

See LVDS-SPI data output for timing and data format of the communication.

1.4.3Backplane for easy connection

To access the interfaces with an easy wiring, the use of the additional backplane is recommended. Especially when using LVDS-SPI, standard cables may be applied, which reduce the efforts for wiring and provide proper shielding.

Three backplanes are available:

• LVDS-SPI / 5HP width (25,4mm)
• CAN / 5HP width (25,4mm)
• LVDS+CAN / 8HP width (40,64mm)

LVDS-SPI Backplane

LVDS-SPI backplane may be used, when no CAN interface is necessary and many CMMs must be integrated on small room. The backplane enables easy connection of the LVDS-SPI interface with standard CAT5…CAT7 cables, while providing proper shielding

Following figure illustrates the options, how to pass data back to the data acquisition system. First option is used for clock rates up to 1,5Mbit/s, second option needs the clock and enable feedback for higher data rates.

CAN Backplane

CAN Backplane may be used, when no LVDS-SPI interface is necessary and many CMMs must be integrated on small room.

LVDS+CAN Backplane

LVDS-SPI and CAN may be both accessed, with the drawback that more room must be reserved for the connectors.