General Functions; Standard Function - Siemens 3RS2 Manual

Digital devices

5.3 Standard function

5.2

General functions

The temperature monitoring relays record the temperature with the aid of temperature sensors
immersed in the medium. The temperature is evaluated by the device and monitored for
overshoot or undershoot of a limit.
For digital devices, the temperature can also be monitored within an adjustable working range
(window monitoring).
The digital device in "standalone" mode is designed for one sensor and can be adjusted by means
of a display menu. In addition to temperature monitoring, this device also offers an effective
option for two- and three-step control. The two-step control allows the devices to be used as
heating thermostats, for example. As three-step controllers, the devices switch over
automatically, for example, between heating and air-conditioning, depending on the
temperature.
The digital device together with the sensor expansion module 3RS2900 (for up to three sensors
with up to two limits) (see Sensor expansion module (Page 63)), is a digitally adjustable system
that evaluates up to three resistance temperature sensors simultaneously. The devices were
developed specifically for motor monitoring (motor windings, motor bearings), but are also very
suitable for other applications with up to three sensors.
Digital devices for one sensor with up to two limits can be used as two-step or three-step
temperature controllers as an alternative to temperature controllers in the low-end area.
Power supply:
The digital device 3RS2600 and the sensor expansion module 3RS2900 (see Sensor expansion
module (Page 63)) are operated with a control voltage of 24 V AC/DC up to 240 V AC/DC,
depending on the version.
The digital device with the IO-Link interface 3RS2800 (see Digital devices with IO-Link
(Page 49)) is supplied directly by the IO-Link Master (L+/L-) or via an external 24 V DC voltage
source. This basic unit can also be operated without IO-Link communication.
5.3 Standard function
Temperature monitoring curve
If the temperature reaches the set limit ϑ1, the output relay K1 will change its switching state.
The output relay K2 correspondingly responds to reaching the lower limit value ϑ2. The delay
time is adjustable.
The output relays return immediately to their original state once the temperature reaches the
respective hysteresis value (automatic reset).
Each of the two limit values ϑ1 and ϑ2 is set for overshoot or undershoot to be monitored. This
means that a limit value is used to output a warning indicating that a limit value is about to be
overshot or undershot. The other limit value results in a disconnection. A two-step or three-step
control can also be implemented with digital devices.
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3RS2 temperature monitoring relay
Equipment Manual, 02/2022, A5E42462552002A/RS-AB/002