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4 TO 20 BOARD FEATURES
The Mercury Instruments 4 to 20 mA board provides two isolated 4 to 20 milliamp current loops, which are individually settable, to track the user-selected item values. Most item values produced by a Mercury electronic instrument can be represented by a 4 to 20 signal. Some of the more common items requested to be represented as 4 to 20 signals are:
Average Flow Rate (Mini-AT and ECAT only)
Instantaneous Flow Rate (Mini-AT and ECAT only)
Dial Rate (Mini-AT and ECAT only)
Gas Pressure (all)
Gas Temperature (all)
Case Temperature (all)
Battery Voltage
Incremental Corrected Volume (Mini-AT and ECAT only)
Principal of Operation
The 4 to 20 mA output board is a peripheral device designed specifically for use with Mercury Instruments’ ECAT, Mini-AT, Mini and ER. The board contains a micro-controller which requires limited programming by the user. An easy-to-use configuration program allows the user to define the following parameters:
Instrument Type (ECAT, Mini-AT, Mini or ER)
Instrument Baud Rate (1200, 2400, 9600 or 19200)
Instrument Access Code
Interrogation Interval (in seconds)
Delay (Hold off Interval)) after failed serial access (in seconds)
Item Code Numbers to interrogate (000 to 999)
Value that is to represent 4 mA (usually 0.0)
Value that is to represent 20 mA (user discretion)
All configuration information is stored in E2PROM to prevent loss of data in case of power failure. While in operation, the 4 to 20 mA output board interrogates the instrument via the RS-232 port on a periodic basis and reads the values of two selected items. If the instrument serial port is busy, e.g. modem or laptop access etc., the 4 to 20 board waits the Hold off period before attempting the next interrogation.
After a successful link to the instrument, the two item values are scaled as a percentage of the 4mA and 20 mA parameters stored during configuration. The upper and lower parameters are configured separately for each loop. The scaled values are then converted to milliamp signals for output to two independent, opto-coupled loop-powered drivers.
Specifications
Designed for a Class 1, Div 2 environment
Operating Temperature –40F to 150F (-40C to 65.5C)
Accuracy of the 4 to 20mA signal +/- 1%
Size: 2-1/2” x 3
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