Connection and commissioning

The sensor cable has 6 cores, the amplifier has only 4 ports?

Some sensors have additional sensor lines.
When the measuring amplifier has only 4 connections for the sensor, you can

  • Do not connect the sensor lines, or
  • switching the sensor lines with the lines for sensor supply in parallel.

The parallel circuit of sensor supply and sensor line is better, because

  • the line resistance of the sensor supply is reduced,
  • the immunity is increased (no open lines)

Where is shield connected?

The shield is to be placed on the amplifier.

When measuring amplifiers with SUB-D15 input jack: to PIN 1.

For amplifiers with SUB-D15HD input jack: on the connector housing
all other measuring amplifier: GND
alternatively when GND eg not available in the connector: on -Us (negative sensor power supply)

Caution: For sensors with connectors of the screen is above the connector housing on the sensor housing.
In this case, it often makes more sense, the screen is not in addition to the measuring amplifier hang up, otherwise there may be transient currents flow over the shield.
It is then better to ground the sensor housing ,

For more information, refer to this document: kb shield.pdf

Note: The bulk of the supply voltage and the ground for the processing analog-digital conversion should be merged at the measuring amplifier.

Expressed differently:

  • A pair of wires supply voltage and ground leads from the power supply to the measuring amplifier.
  • A line pair output and ground leads from the measuring amplifiers to the AD converter.

How can I reduce noise on the output signal?

  • Merging the mass of the power supply and the ground of the analog-digital converter at the terminal of the measuring amplifier. "All lines as a pair for and embarrassed by the measuring amplifier"; GND to the measuring amplifiers GSV-1 and GSV-11 is then used twice!
     
  • The quality of power supply is crucial for the quality of the output signal.
    • The measurement technique should have its own power supply,
    • A switching power supply may cause interference. Better use a linear power supply in case of doubt.

 

For more information, refer to this document: kb shield.pdf

Over the entire range of force sensors or torque sensors, a signal ratio is achieved to noise between 1000/1 to 10000/1 (at a bandwidth of 250Hz) with analog amplifiers usually.

What are the other measures to reduce noise?

  • own power supply for sensors and actuators
  • own cable channel for sensor and actuator
  • Terminator 10k or 1k at the analog input of the PLC or of the AD converter. The electronics of the ME-measurement systems have 50ohm output impedance and can therefore be loaded. The error by loading the output is usually negligible.
  • In some AD converters, it is necessary to carry out oversampling and subsequent averaging. The variance in AD converters according to the SAR method Successive approximation can be quite high ...

What is the relationship between the mechanical input signal and electrical output voltage?

We consider the entire measuring chain consisting of sensor and amplifier:

Respectively the slopes of the curves are given for the sensor and the amplifier.

the sensor for example 2,000 mV / V per 100.0 N
at the measuring amplifier for example 10.00 V per 2,000 mV / V

Messverstär sensor and are connected in series, the characteristic values ​​are therefore multiplied together:

  • 2,000mV / V / 100,0N x 10,00V / 2,000mV / V = ​​0.1 V / N
  • 10N corresponds 1V
  • 100N corresponds 10V

NOTE: The slope of the sensor characteristic is referred to as "characteristic". The characteristic value is always given as output at (pro) nominal power

the slope of the amplifier characteristic is referred to as "input sensitivity". 100% of the output signal is obtained at the input sensitivity.

The zero signal of the sensor (output at 0 power) and the zero signal of the amplifier (Ausgangsgssignal at 0 input voltage) are not included in the calculation. With the zeroing function, this constant error is matched.

How to calculate the characteristic when current output is 4-20mA?

When current output 4-20mA, the zero point is shifted to 4mA.

The maximum change of the output signal (the output signal swing) is 16mA.
The output increases by 16mA if the input sensitivity is modulated at 100%.

Sensor: 2,000mV / V 100N per
amplifier: 16mA per 2,000mV / V

  • 2,000mV / V / 100,0N x 16mA / 2,000mV / V = ​​6,25N / mA
  • 1mA (+ 4mA offset) corresponds therefore 6,25N
  • 16mA (+ 4mA offset) corresponds therefore 100N

Hindweis: Even when measuring amplifiers with shifted zero, for example, 5V ± 5V input sensitivity for the output signal is stroke indicated.