The calibration check signal is a low-active, digital switching signal that is used to generate a defined detuning of the measuring bridge. In the the project planning of a force transducer, it is possible to specify how large this detuning should be from the zero point, naturally only within the tolerance range of the amplifier.

It is highly recommended to always use amplifiers with a current output and to arrange a corresponding load resistor at the input of the evaluation unit, at which the required input voltage then drops due to the current flow. Currents can be transmitted without loss over longer distances, which cannot be achieved with voltages. The line is checked by the zero point current which is greater than "zero" mA.

When using a force transducer with an internal calibration check, the connection of the CC contact to ground (GND) forces the signal current of full load at the output of the sensor amplifier (e.g. 9 mA or 20 mA) when the sensor is unloaded. This can be used to check the functionality of the calibration switch-off device without a real load on the sensor.

Example of using the calibration check signal to check the shut-off chain

By activating the calibration check signal, a defined detuning is generated directly at the measuring bridge. This results in a defined signal deviation at the output of the measuring amplifier. As the deviation reaches at least the maximum value of the sensor current, the cut-off relays must subsequently assume the overload state. This method can be used to test the cut-off chain using an external unit or a manual test.

The following are checked

• Correct connection to the strain gauge measuring bridge
• Functionality of the measuring amplifier
• Switch-off function of load limiters
• Correct external wiring of the switch-off circuits

Tip:

The calibration check signal can also be used for online monitoring of the sensors if required. However, the measuring range of the evaluation device must be selected large enough for this. Example for a sensor with amplifier 4...20 mA:
By loading the sensor, 20 mA must be measured at the output of the sensor. When the CC signal is connected, the measurement signal jumps by 16 mA, resulting in a signal of (20+16=) 36 mA.

=> If the measuring range permits a signal of 36 mA, the sensors can be monitored online with an amplifier!

Example for determining the required measuring range:

for a sensor with amplifier 4...20 mA
=> CC signal generates a jump of 16 mA
=> 4 mA zero point + 16 mA CC step = 20 mA absolute

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