SRV EX Installation without temperature

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


the SRD needs temperature input to the electronics so either the temperature sensor built 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 Manual 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:

  1. 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, Uo

7.14 V

Output current, Io

729 mA

Output power, Po

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.


Reference


Rheonics EX installation manual: https://rheonics.com/resources/manuals/

Article: Is it still possible to measure viscosity without connecting the PT1000 to our SRV?