CMM III

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.

The following section describes the functionality of the internal measurement and every interface.

2.1Current measurement

2.1.1Measurement procedure

The current is measured internally at a sampling rate of 375kS/s, where 9 samples are averaged to 1 “external” sample. Thus, an “external” sampling rate of 41,667kS/s is achieved.

The current range is selected automatically, when CMM is switched on. Range selection does not influence the output voltage. Except large current changes of several amperes will result in short time voltage drops of few 100 mV. See Dynamic behavior for dynamic behavior.

For every interface (RS232, CAN, LVDS-SPI) an independent averaging is implemented, which starts averaging with every readout. Following figure illustrates the averaging.

I.e. if CAN sends its message every millisecond, around 42 external samples are averaged, which are already an average of 9 internal samples each.

Averaging from readout to readout does not influence the averaging on other interfaces. I.e., averaging is independent for

• RS232
• CAN
• LVDS-SPI

An overflow of the averaging may not occur even after a year of readout interval.

2.1.2Reverse current detection

Reverse currents can’t be measured, but a flag is signaled, when a current of several 100mA is applied in reverse direction. The output data on CAN or LVDS-SPI is an invalid number, exceeding the measurement range (0xEEEEEEEE in hexadecimal representation).

2.1.3Dynamic behavior

Switching between the ranges occurs very fast from low current range to high current ranges within less than 1µs (500ns typical) after the current range has been exceeded.

The following figure shows the typical behavior at a current step from some µA to more than 60 amps.

• yellow trace: current through the module
• Red trace: voltage drop over the module

The ring at the voltage drop results from the inductive component of the applied load.

The following figure shows the zoom of positive and negative edge of the current step.

Conclusion: The voltage drop while switching occurs is well below 1V for a duration of some microseconds maximum.

2.2ON/Off control

CMM_III may be switched on or off by a hardware input or by software. The following parameters can be adjusted by configuration:

• Active level (high or low) of the hardware input
• Priority of hardware or software on/off-control

Configuration may be changed by the command ONMOD=x via RS232 or CAN using ISO-TP protocol, while x one of the following numbers 0…7:

2.3CAN data output

CAN data is sent cyclically on a specified CAN ID. This CAN ID is adjustable by RS232 configuration.

Content of the transmitted CAN message is as follows:

Current is returned as 32 Bit unsigned long value in steps of 100nA split into the first 4 bytes of the CAN message.

When CMM_III is in off state, the returned value is 0xFFFFFFFF, which represents 429.4967295 A, which is no valid measurement value.

When CMM_III is in on state, but reverse current is applied, the returned value is 0xEEEEEEEE, which represents 400.8636142 A, which is no valid measurement value.

2.4LVDS-SPI data output

The measurement value can be read via an SPI-interface on LVDS level. SPI yields high data rates, while LVDS level yields low noise radiation and higher noise immunity, due to differential signaling.

The protocol for reading data of a single current measurement module is as follows:

When several modules are connected in daisy chain, the data from the previous module is forwarded to the output as following figure illustrates:

When En_In is asserted, the module sends out its current value during the next 32 clock cycles with MSB first. After 32 clock cycles the received data word is forwarded. En_In must be valid for 32 clock cycles, multiplied by number of CMMs in the chain. The current is returned as 32 Bit unsigned long value in steps of 100nA.

2.5RS232 data output

The measurement value is sent over RS232 in the interval of 100ms. The interval is adjustable via RS232 configuration. Connect the PC’s COM-Port to the RS232 at the front cover with a simple 1:1 Sub-D-Cable (no Null modem). Use a standard terminal program with the following settings:

• 9600 Baud
• No parity
• 1 Stop bit
• No Handshake

You will see the module’s output as following picture illustrates:

• R = Range
• I = average current in µA since last readout
• Min = minimum current in µA since last readout
• Max = maximum current in µA since last readout

Every Line is terminated by “Carriage Return / Line feed” to separate between new data.

2.6RS232 configuration

Configuration of the module using RS232 gives access to the CAN transmission configuration and the send interval for RS232-interface data output. Connect the PC’s COM-Port to the RS232 at the front cover with a simple 1:1 Sub-D-Cable (no Null modem).

Use a standard terminal software with the settings:

• 9600 Baud
• No parity
• 1 Stop bit
• No Handshake

You will see the module’s output as shown in RS232 data output.

By sending the commands of the following table the settings may be queried. Every Command must be finished with a carriage return / line feed (\r\n). I.e. every command string needs to have the following format similar to the following example: SINTV?\r\n

• \r is ASCII character 0x0D
• \n is ASCII character 0x0A

By sending the commands of the following table the settings may be set. Every Command must be finished with a carriage return / line feed (\n\r). I.e., every command string needs to have the following format like the following example: SINTV=100\n\r

Furthermore, the following additional commands using RS232 are defined. The commands also must be finished with \r\n.

2.7CAN configuration

Configuration of CMM may be performed using the CAN interface. For this configuration ISO-TP protocol is applied, according to ISO 15765-2. Normal addressing mode is used.

Configuration is performed by sending commands to CMM. Every command is acknowledged by a response.

2.7.1ISO TP Header

Single frame commands

Most commands and responses fit into a single CAN message. I.e. single frames according to ISO-15765-2 may be used. The respective CAN message carries the following data:

Multiple frame commands

If more than one message is necessary for a command, first frames, flow-control and consecutive frames are used in the following order from top to bottom:

If the multiple frame message is a response, exchange the CAN-IDs TPRID and TPLID.

Data Byte 1/2 xx_N_PCI

Data byte 1 contains frame type and data length information according to ISO 15765-2.

For single frames the values 0x04…0x07 are valid, which represent the number of following data bytes. 4 bytes minimum for Command, Action, Error-code, and Reserved - 7 bytes maximum including 3 command depending data bytes.

For first frames 0x10 in byte 1 is added to the command length, which can be found in byte 2.

For consecutive frames 0x20 is added to a message counter in byte 1.

2.7.2Command Header

Data Byte 2/3 Command

Byte 2 for single frames, byte 3 for multiple frames

Data Byte 3/4 Action

Byte 3 for single frames, byte 4 for multiple frames

Data Byte 4/5 Error-code

Byte 4 for single frames, byte 5 for multiple frames

This data byte is only valid for responses from CMM. In commands to CMM this byte should always be 0x00 = No error.

Data Byte 5/6 Reserved

Byte 5 for single frames, byte 6 for multiple frames. This byte is reserved for future use.

2.7.3Command overview

Following commands are available:

Please note, that only command header and command dependent data is shown. ISO 15765 header must be added, and messages must be split into several messages, if necessary.

2.7.4Response overview

Every command is acknowledged by a response.

Most commands are executed first and send a response after execution. Exceptions from this rule are as follows:

• RESET:
  • The response is sent immediately.
  • Reset is performed afterwards.
• TPLID, TPRID:
  • The response is sent with the previous CAN ID.
  • Respective CAN ID for ISO-TP is changed after the response has been sent.
• CANBD:
  • Baud rate is changed after response has been sent.
  • Please note, that bus errors may occur after baud rate has changed. CMM should be restarted afterwards.

Negative Responses

Negative responses are returned when a failure occurred. I.e., the command was invalid and has been rejected.

Positive Responses

Positive responses to the respective commands are as follows. Please note, that only command header and command dependent data is shown. ISO-TP header must be added, and messages have to be split into several messages, if necessary.

Command dependent data of the GLVAL response:

2.7.5Example CAN traces

The following CAN traces should help to understand the tables above. The command and responses are marked in the respective colors: Command / Response. Please note, that flow control frames are integrated in the respective command or response, but they are sent by the respective counterpart.

CMMON: switch ON

CMMON: switch OFF

SWVER (Read SW Version)

SINTV (set serial interval)

IRS recommends a recalibration within 2 years.

The calibration should be performed at multiple calibration points for all 7 ranges. IRS recommends measuring at least the following currents:

CMM values should be captured with the RS232 or ISO-TP function GLVAL. This function returns the value averaged since last read.

Before capturing a valid value, enable the calibration current, perform a dummy read and wait 100 ms.

The fluctuations of the power source used should not exceed 0.1% of the nominal value.

4.1Version 2.2.0

• At least 6 samples will be ignored after range changed no matter if up or down
• Added command to temporary change the count of ignored samples after range changed (RCISC)
  • Each range switch will cause a peak in min/max value (and a small error in the average value).
  • This command can be used to minimize that behavior
• Added command to temporary change the minimum range (MINRG)
  • Each range switch will cause a peak in min/max value (and a small error in the average value).
  • This command can be used to minimize that behavior by reducing count of range switches

4.2Version 2.1.3

• Some samples will be ignored after range changed (Up: 4 Samples; Down: 6 Samples)
• Update to support an alternative operational amplifier (original one was out of stock)
• Update to support a controller type with less memory

4.3Version 1.3.0

• Added command for averaging min./max. value (MMASC)
• Added command to save user defined text (UTEXT)

4.4Version 1.2.7

• Added command to query the serial number (SERNB)
• Added command to query the calibration date (CDATE)