SRV EX Installation without temperature

SRV can be used without temperature connection to the electronics. Operation of sensor does not depend on the temperature and hence a temperature input is not required.

SRD needs temperature input to the electronics so either the temperature sensor inbuilt in the sensor is used or an external Pt1000 can be connected to sensor electronics. It is also possible to write temperature of the sensor from an external probe over Modbus.

This article focuses on using SRV without a temperature connection. This could be the case when the EX barriers that are needed for Pt1000 are not available or the customer does not want to use 2 additional barriers that are needed for the Pt1000 connection.

Ex Installation diagram without temperature

The figure below shows the diagram for the connection. It is taken from the EX installation manual (Figure 10 from version 2.0 of manual).

1	M12 cable connector female, rear view
2	Sensor:M12 connector male, front view
3	Ground tab (optional)
A	Safe Zone
B	Intrinsically safe cable
C	Hazardous Zone

Zener barrier specification

The Zener diode barrier connected to the transducer coil circuit must meet the following specifications (Table 4 from EX installation manual version 2.0):

Transducer coil circuit Zener diode barrier specifications

Max. output voltage	Uo	< 7.3	V
Min. series resistance	Ro	> 9.8	Ohm
Max. output current	Io	< 730	mA
Max. output power	Po	< 1.3	W
Fuse rating		<=200	mA

This Zener diode barrier must have two channels, one for each conductor of the transducer coil circuit.

Commercial Zener diode barriers that fulfill these specifications are inTable 6 from EX installation manual version 2.0:

For transducer coil circuit:

Pepperl + Fuchs Z757

Specification of commercial Zener diode barrier suitable for transducer coil circuit

Series resistance	9.8 ohms, min.
Fuse rating	200 mA
Maximum safe voltage	250 V
Output voltage, U_o	7.14 V
Output current, I_o	729 mA
Output power, P_o	1.3W

Notes on temperature output

Even though there is no direct measurement of temperature from the probe when the temperature leads from the probe are not connected to the electronics, the sensor does estimate a process temperature based on the frequency characteristics of the sensor. This estimated temperature is only to be used as a guide as it can be influenced by deposits. This estimated temperature replaces the measured temperature in the output strings of the sensor so you will still see a temperature output from the sensor.

Note:

Only for Ex Sensors. Power Input: 240V Maximum AC Single Phase, this is exclusive for Ex sensor configuration and would be the best to protect the zener barriers used in the configuration, only single phase power supplies should be used.