Transducers with Frequency Output

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

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

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 impendance 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 impendance 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.

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.

For calibration of measurement range and zero point see General Operating Instructions

For EMC and cabling guidelines see Cabling and Installation Requirements