Electronic Safety Limit Thermostat (Slt) - Siemens LMS14 User Manual

Basics of electronic safety limit thermostat (SLT)
Error handling
Building Technologies Division
6.11.28

Electronic safety limit thermostat (SLT)

Warning!
If the safety limit thermostat (SLT) has the bridge resistor fitted (with LMS14...:
R13SC), an external limit thermostat (LT) must not be connected since its cutting
out in the case of overtemperature would not lead to shutdown so there would
be a risk of excessive boiler temperatures.
Units using a safety limit thermostat (SLT) with bridge resistor fitted require a
flow and a return sensor (mandatory) and a suitable parameter set to provide a
reliable Switch-off function (safety limit thermostat (SLT)).
If not observed, there is a risk of excessive boiler temperatures.
The electronic (S)LT of the LMS14... consists of function blocks which provide the
following functions:

Shutdown in the event of overtemperatures

Performance of a number of plausibility checks, enabling the system to intervene in
the process in due time to avoid overtemperatures

Checks aimed at detecting faulty states and triggering appropriate actions
Warning!
The 2 sensors used in connection with the (S)LT (flow and return sensor) are
safety-related!
These 2 sensors are to be located and fitted such that constant and reliable
heat transfer is ensured (during the whole time of usage and after
replacement).

Sensor B2 must be fitted in a location where it acquires the effective maximum
boiler temperature!

The return sensor must be fitted in a location where it acquires the effective boiler
return temperature!
When fitting the flow and the return sensors, note the following:

Clamping bands are not permitted!

When using a holding spring for fixing, additional strain relief must be provided!

Screwed immersion sensors can be fitted with no need for taking any additional
measures
Note!
Adequate measures may be required for checking the heat transfer inside the boiler.
Parameterization must be matched to the type of boiler(s) and the type of plant!

The relevant regulations for boiler and plant must be observed!

We recommend to use an external safety limit thermostat in the following cases:
- Boiler capacity >120 kW
- Applications with pressure class 3
The following table lists the types of errors that can occur. Also shown are the relevant
error reactions, that is, whether startup will be prevented or lockout triggered.
User Manual LMS14...
6 The settings in detail
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CC1U7471en
07.05.2014