Transducers with Frequency Output

General Description

These measurement transducers convert an input current, an input voltage or the signal from a sensor (thermocouple, Pt-100, resistor, measurement bridge, etc.) into a frequency which is proportional to the magnitude of the input signal. The programmable version has DIL switches to set the maximum output frequency in steps of 100 Hz. (max. 20 kHz). The frequency outputs from different modules can be connected to a common bus.

  • Direct conversion of an input signal (voltage, current, all common sensors) into a frequency output which is proportional to the magnitude of the input.
  • Suitable for SPC and other systems with frequency or counter inputs, analog signals with AD-converters are not necessary.
  • Optional galvanic isolation between the input, output and power supply (3 port isolation)
  • Output frequency up to 20 kHz (can be selected via switches in the programmable version), impulse amplitude is selectable via a voltage at the "enable" input
  • Where there are several modules, it is possible to connect them to a common frequency bus: only one frequency input is necessary, modules are selected by an "enable" input

Overview

Housing

Modules for DIN-Rails

Type Input Range Supply
RTMF 70 Pt-100, resistor fixed 19-30 V
TCMF 70 Thermocouple fixed 19-30 V
SIGV/IF 70 Voltage, current fixed 19-30 V
SCMF 90 Measurement bridge progr. 19-30 V

Other modules (e.g., programmable RTM-, TCM modules or SIGVI modules), printed circuit board modules and other accuracy classes are available on request.

Type:

The type designation is equivalent to that for modules with a voltage output, but with an "F" before the module number. For all Pt-100 or resister modules, the 3-wire versions are denoted XXXF 71 or XXXF 11. The technical data (input, range, supply, etc.) are, apart from the fact that they have a frequency output, identical to the basis module (accuracy class D) (other accuracy classes are available on request). Example: TCMF 70-K is a module for type K thermocouples; RTMF 71 is a modules for Pt-100, 3-wire connection.

When ordering, please specify:

  • Module type
  • Input range (in V or mA)
  • Output range (in Hz or kHz)
  • Supply voltage (in V)
  • Options: programmable frequency output, DC-DC converter for the supply (3 port isolation). If desired, the module can be delivered already precisely set-up for a specific range.

Technical Data

Specifications for Frequency Output (Maximum values at 25°C)
General Accuracy Class D Unit
Transmission error (linearity)1 0.02 %
Temperature drift 100 ppm/K
Output impedance, typ. 600 Ohm
Output amplitude, typ.2 15 V
Influence of operating voltage 0.02 %/V
Temperature range, recommended 0/60 °C
Temperature range, operable -20/90 °C

1 The transmission error applies to a frequency of 10 kHz.
2 The quoted output amplitude is given for a load resister, R1, of 1 kOhm and for 24 V at the "enable" input.

Accuracy of the Frequency Output

Basic error of max. 0.2% (incl. transmission error, calibration error and drift between 20-30°C). On delivery, the outputs of the measurement transducers are set to 5 kHz (max. 0.2% error). The calibration can alter slightly when the range is switched (SMD switches), switching error typ. 1% (max. 4% for 100, 200, 400 and 800 Hz).

Input/Measurement Range

  • The input stage (connections, technical data) of the frequency output modules is identical to that of the basis modules with voltage output.
  • Basis module with fixed range: most measurement ranges are available (specify when ordering), for more information see the documentation for the corresponding basis module.
  • Programmable basis module: measurement range and zero point selectable by switches, (intermediate values set using a potentiometer), for more information see the documentation for the corresponding basis module.

Power Supply

The power supply for this module is the same as for the basis module, current consumption is around 20 mA greater. Bipolar power supply is not possible. A galvanically isolated power supply is available as an option (uses DC-DC converter). 3 port isolation is thus achieved (not suitable for mains voltages).

Frequency Output

Square impulses, amplitude determined by the voltage at input 3 (enable). The output impedance is around 600 Ohm (protection against short circuits and interference voltages). When the load resistance is 1 kOhm, a voltage splitter arises (600 Ohm/1 kOhm), which correspondingly reduces the voltage amplitude (to approx. 15 V for 24 V at the enable input). The galvanically isolated output stage eliminates earth loops and varying ground potentials. It is NOT suitable for mains voltages (max. 60 V). See the operating instructions for more information.

Frequency Range

The output frequency varies between 0 Hz and the max. output frequency, according to the magnitude of the input. In the programmable version (option), the maximum output frequency can be set via switches, in steps of 100 Hz (up to a max. of 20 kHz)

Options

  • DC-DC converter (built into the module) for galvanic isolation of the 24 V power supply, test voltage of 700 V, max. operating voltage 60 V.
  • Programmable cut-off switch (built into module) for monitoring, control.
  • Other dimensions (ranges, input, output, time behavior).

Operating Instructions

1. Connections (screw terminals)

1: Power supply + (24 V DC)
2: Power supply - (GROUND)

3: Enable frequency output (4 -30 V)
4: Frequency output (impulse), load with 1-5 kOhm

TCMF70/90 (connections as TCM70/90):
5: Open
6: Open, test: short circuit with 7 disables cold solder joint compensation
7: Thermocouple -
8: Thermocouple +

RTMF70/71/90 (connections as RTM70/71/90):
5: Se-
6: So-
7: Se+
8: So+

SIGFV/IF70/90 (connections as SIGV/I70/90):
5: Open
6: Open
7: Input -
8: Input +

SCMF70/90 (connections as SCM70/90):
5: Bridge supply +
6: Bridge supply -
7: Input -
8: Input +

Connecting the Frequency Output of a DIN-Rail Module, with Galvanic Isolation

Connecting the Frequency Output of a DIN-Rail Module, with Galvanic Isolation Fig. 1: Connection of a frequency counter, enable voltage galvanically isolated from module voltage. The load resistance should be between 1 kOhm and 5 kOhm (including the input impedance of the frequency counter). The galvanic isolation prevents earth loops and eliminates the problem of different earth potentials. It is NOT suitable for mains voltages (max. 60 V).

Connecting the Frequency Output of a DIN-Rail Module, no Galvanic Isolation

Connecting the Frequency Output of a DIN-Rail Module, no Galvanic Isolation Fig. 2. Connecting to a frequency counter, enable voltage taken from the module voltage (24 V), no galvanic isolation.

2. Frequency Output

Figures 1 and 2 show the connection of the frequency output (4) to a frequency measurement unit.

For versions with an opto-coupler output and at frequencies of more than 3 kHz, the selection of the load resister, Rl, is of great importance: it should lie between 1 kOhm and 5 kOhm (including the input impedance of the frequency counter). The precise value of the load resister, Rl, may be adapted according to circumstances and from case to case. For a small load resistance (1-2 k), the lower value of the frequency output will be correspondingly small, and the total amplitude will be reduced (Uhigh - Ulow), the output impedance is around 600 Ohm. At larger load resistances the output impulse may not be able to drop as low as the desired "low" value, Ulow. Example for f = 5 kHz, Uen = 24 V and Rl = 2 kOhm: Ulow is approx. 0.5 V, Uhigh approx. 18 V. For f = 5 kHz, Uen = 5 V and Rl = 3 kOhm, the corresponding values are: Ulow = 1.2 V, Uhigh = 3.6 V. We recommend a load resistance of approx. 1 kOhm for frequencies greater than 10 kHz. At 12.8 kHz, Uen = 24 V and Rl = 1 KOhm, Ulow is approx. 0.5 V and Uhigh approx. 14 V. At 20 kHz and Rl = 1 kOhm, Ulow is approx. 1 V and Uhigh approx. 14 V.

The use of coaxial cable introduces an additional load to the frequency signal and smaller amplitudes can result.

The enable input (3) requires a voltage, Uen, between 4 and 30 V. If the input is open or if a voltage of approx. 0 V is applied then the frequency output is disabled (e.g., during bus operation). This voltage determines the amplitude of the frequency impulses (reduced by voltage drops in the transistor and protection elements), see section above. The protection elements have a resistance of typ. 600 Ohm.

3. Bus Operation/SPC Connection

Several modules can easily be connected to one frequency input. In this case, all frequency outputs (4) are connected together (bus) and to the frequency input, see Figure 3. The individual enable voltages can be generated via an I/O component. Important: the ground of the I/Os must be connected to the ground of the frequency input, the load resistance should be connected as shown in Fig. 1.

Connection of multiple modules Figure 3. Connecting several modules to the same frequency counter. In order to switch the output of a module to the bus, the enable input (3) must have a positive voltage between 4 and 30 V. The Uen voltage determines the amplitude of the frequency impulses (reduced by the voltage drops in the protection elements (typ. approx. 600 Ohm). The load resistance, Rl, should lie between 1 kOhm and 5 kOhm, depending on the frequency range.

Further Information