GWA – 250
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Application
The limit value switch
GWA – 250
is used for supervising electrical standard signals 0...10V / 0...20mA resp.
4...20mA or temperature resistors Pt100 regarding transgression resp. underrun of limit values.
The device allows it, additionally to continuous measurements, to set up to two switching limits without the need
for additional measurement devices.
The version GWA – 250 is suitable for supervision of supply and control voltages, e.g. in the water and waste
water industry for filling level monitoring and pump control (e.g. 15% pump on, 95% pump off).
The version GWAP – 250, for connection of a temperature resistor Pt100, can be used for supervision of
process temperatures in all fields of industry.
Alternatively to the on-site operation, where the key coding switches for setting the switching limit are integrated
in the device, the version S is available, where the key coding switches can be installed separately from the
device, using them as remote control. These are suitable for the installations into control cubicle doors resp.
front panels.
Function
Measuring principle
Version GWA – 250 / GWAS – 250
The connected electrical standard signal 0...10V / 0...20mA resp. 4...20mA is compared by the evaluation circuit
with the set limit value at the key coding switches in % of the nominal signal range (10V / 20mA / 16mA), with
reference to the respective signal zero value (0V / 0mA bzw. 4mA).
Examples:
At standard signal 0...10V the setting 50% equals a signal voltage of 5V
At standard signal 0...20mA the setting 50% equals a signal current of 10mA
At standard signal 4...20mA the setting 50% equals a signal current of 8mA (50% of 16mA) + 4mA = 12mA
The connected signal device at the input can be powered by the integrated measurand transducer supply.
Version GWAP – 250 / GWAPS – 250
The voltage drop at the connected temperature sensor Pt100 is compared by the evaluation circuit with the set
limit value at the key coding switches in % of the set temperature signal range (30K / 50K / 100K / 600K), with
reference to the set signal zero value (-50°C / 0°C / +50°C).
Examples:
At zero value –50°C and range 100K the setting 50% equals a temperature of –50°C + 50K = 0°C
At zero value 0°C and range 600K the setting 50% equals a temperature of 0°C + 300K = 300°C
At zero value +50°C and range 30K the setting 50% equals a temperature of +50°C + 15K = 65°C
The connected Pt100 in 2-wire resp. 3-wire technology is supplied be an internal constant current source and is
supervised for wire break or short circuit.
Signal evaluation
The transgression resp. underrun of the set limit value causes the switching of the relay resp. the relays
depending on the configured safety function (minimum resp. maximum safety) resp. operation function (double
limit value function resp. two-position-control function).
The switching state of the relays is indicated at the front side of the device by two red LED’s.
Switching delay
In some applications it is necessary to compensate heavy signal fluctuations that may be produced by mixing
machines or at fill-in resp. emptying of containers, to avoid spurious switching actions.
Two switches inside the device allows the configuration of a switching delay of 0,4 s or 4 s, separately for each
output relay, at activation and deactivation of the respective output relay.
