Rototherm - Model Series 800 Smartstat -Electronic Pressure Switch & Transmitter
The Series 800 Smartstat is a microprocessor controlled pressure switch, transmitter and indicator, which enables several instruments to be replaced with a single device.
- Pushbutton calibration of set points and transmitter range enables calibration on site without tools.
- Programmable switching delays - the switching on or off (or both) of the relays may be delayed from 0.5 seconds to 15 minutes. This is particularly useful for preventing unwanted switching due to temperature transients.
- Display of maximum and minimum pressures recorded by the Smartstat.
- Display of transmitter output in mA.
- Displayed units of measurement - can be changed by the user as required.
The input pressure applied to the Smartstat is converted to a proportional electrical signal by the silicon pressure sensor. After amplification this signal inputs directly into the analogue to digital (a/d) port on the microprocessor.
The microprocessor continuously calculates the pressure from the input signal, compares this to the switch setpoints and operates the relays as required. If the pressure rises above the UPPER switch point the relay changes over from normally closed (NC) to normally open (NO), as the pressure falls below the LOWER switch point the relay changes over from NO to NC.
In addition the microprocessor updates the LCD display of the pressure and the status of the relays. The typical response time of the relays to an alarm condition is about 125mSec.
Should the 24Vdc power supply fail (or fall below 12 volts) the relays can be configured to remain in their current position or switch to the NO or NC position. This is the ‘Fail State’ that is indicated on the LCD.
A separate watchdog timer (WDT) continuously monitors the operation of the microprocessor. In the unlikely event that the processor ‘hangs’ this is detected by the WDT which re-boots the processor, restoring normal operation within 3 seconds.
Entry of the switching points, the Fail State and switching delays for each relay is carried out using the pushbuttons on the front of the Smartstat. An access code must be entered first to ensure that there are no unauthorised changes.
The pressure settings for each relay are adjustable throughout the range enabling the switching differential to be varied from just one digit, up to 100% of the range. All of the information entered is stored on an EEPROM so that it is retained when the power supply is off.
The pushbuttons on the front of the Smartstat are also used to calibrate the transmitter output. An access code must be entered first to ensure that there are no unauthorised changes. The ‘start of range’ and ‘end of range’ can be input and 4-20 mA or 20-4 mA selected. If the transmitter output is not required it can be disabled, resulting in a constant supply current of 3.5mA to the Smartstat. The maximum and minimum pressures applied to the Smartstat can be displayed by pressing the MAX or MIN pushbuttons. These values can be reset to the current pressure by holding down the appropriate pushbutton for 15 seconds.
The relays are optional on the Smartstat and can be obtained at a later date and easily fitted by the customer.