ibaBM-DP has a measuring transducer (8 Bit, sampling rate 10 ns) that enables you to measure the bus voltages. The measured voltages are displayed as bar diagram in the I/O Manager. The bus voltages can also be acquired as signals. For this purpose, use the "Slave diagnostics" module, see chapter Slave diagnostics module and Diagnostic modules.

Measuring principle for determining the bus voltages


For determining the voltage difference between high and low level, one voltage value will be determined in the high and low status each. The difference is the measured value for the level height.

The measurement in the high status is done in situations, where the level is at high for at least two consecutive bits after the level has changed from low to high. The values are measured at the end of the first bit. Thus, a nearly steady state of the level at the time of the measurement can be assumed.

The measurement in the low status is done according to the same principle, i. e. in situations where the level is at low for at least two consecutive bits after the level has changed from high to low.

With an increasing transfer rate, the number of available measurement values decreases as the time period of one bit is getting shorter and shorter. Moreover, the time of measurement within one bit has a Jitter. With an increasing transfer rate, this Jitter becomes more and more relevant as the voltage does not reach a steady state anymore. Thus, the precision of the measurement gets lower at high transfer rates.

The measurement is only done for status telegrams which are exchanged between master and slaves. Depending on the bus cycle (depending on the transfer rate and the number of participants), the update rate of the bus voltages can be in the seconds range. The ibaBM-DP hardware does not allow for a more frequent measurement. The focus of the voltage measurement in the ibaBM-DP lies on the statistic evaluation of the voltage ratio on the bus and the long-term acquisition of the voltages. The measurement of the bus voltages in ibaBM-DP is not suited for acquiring and analyzing fast processes on the bus voltage.
Bar chart for the bus voltages

The bar chart of the bus voltages becomes visible when you select the bus node “X40: Bus 0” or “X41: Bus 1” of an ibaBM-DP in the I/O Manager.

The currently measured bus voltage is displayed as a bar for each device on the bus. The following areas are differentiated by color:

  • Green: Participants with a voltage in the range between 4.0 V and 7.0 V are generally called “okay”.

  • Orange: Participants with a voltage in the range between 2.5 V and 4.0 V may be okay. Line losses due to a long length of the conductor between ibaBM-DP as point of measurement and the participant, may result in a lower voltage. Also, a problem with the participant itself may result in a lower voltage.

  • Red: Participants with a voltage lower than 2.5  V are generally designated as “not okay”.

  • Gray: Slaves that do not exist but are configured are displayed as gray bars at the corresponding position. In the overview of the bus participants above, these slaves correspond to the red marked slave symbols.

The dotted rectangles show the range between the minimum and maximum value of the bus voltage. Minimum and maximum value are only determined as long as the bar diagram is visible in the I/O Manager. When you leave the bar diagram view, the values will be reset. The values can also be reset manually with a click on <Reset min/max voltage windows>.

Clicking on the grey triangle displays additional participants.
Save bar chart as image

For further use, the bar diagram can be saved as image or copied to the clipboard. Open the context menu with a right mouse click in the bar diagram and select Copy to clipboard or Save as image. The image formats PNG, GIF, JPG, TIF, BMP are supported.