Using the RS-485 Port of S2A/SC-200 LVDT Signal Conditioners

HGSI’s LVDT signal conditioners incorporate an RS-485 two-wire multi-drop serial communications interface for up to 16 devices. This port enables half-duplex serial communication by which a module can be set up and calibrated remotely and system data can be read or stored on a PC running an ASCII terminal program like Hyper Terminal with a 2-wire RS-485 converter for the computer's com port or USB port connected to terminals J3-1 and J3-2 of the signal conditioner.

The PC's com port parameters are: 9600 bps, no parity, 8 data bits, and 1 stop bit (9600, NP, 8, 1), with echo on and no flow control. Be sure that the RS-485 connection for Data A (D-) is connected to J3-2 and Data B (D+) is connected to J3-1. Always follow the data polarity (D) indicated above, regardless of the letters for data lines used by the RS-485 converter.

HGSI offers a 1.8 m long 2-wire USB-to-RS-485 converter cable, USB-RS485-WE, p/n 5810-0001, having an orange wire with a red tip plug that is Data B (D+), and a yellow wire and tip plug that is Data A (D-). Normally no driver is needed for a USB-RS485-WE used with MS Windows 7 or later. In most cases, the optimum driver for any particular OS is the VCP version.

RS-485 user commands for S2A / SC-200 HGSI LVDT signal conditioner modules

Note: that all commands must be formatted to begin with UXX followed by a space, where XX is the numerical value between 00 and 15 of the module's decimal digital address as set up on DS2, switches 5, 6, 7, and 8 according to Table 1b in the S2A instruction manual, or by following the DIP switch settings diagram shown on the S2A module's left side label.

Note: Some Set command descriptions show in bold face the range of values that follow the command and a (space).

Analog In RUN mode, returns the nominal analog output value scaled in electrical units that depend on the setting of DS1, or the analog output range selected with the Set Aout command.

Cal Enters CALIBRATION mode; command is the same as pressing FULL SCALE and ZERO pushbuttons together.

Clrall In RUN mode, clears EEPROM of all RS-485 command settings used to override module's DIP switch settings.

Config Lists the module's setup data and displays DIP switch settings and current EEPROM values. Specifically, it shows the module's firmware version, operating mode, digital address (00 - 15), date stamp, serial number, analog output setting (1 - 8), excitation frequency setting (0 - 3), output invert switch off or on, low frequency filter status (LF) off or on and filter corner frequency, excitation drive jumper (J7) in or out, failure output delay time (FD) and polarity (FOP) NC or NO, Lock status, and stored EEPROM values for ADC Lo, ADC Hi, Input pot, and Gain pot. (Log and store all Config data and values by digital address to be able to reconfigure a hot swapped module at a later time).

Error In RUN mode, displays any setup or operations error code(s); for multiple errors, the error code sum is displayed.

Errsec In RUN mode, ON, OFF (default) toggles error indications and failure outputs from low DCR LVDT secondaries.

Errsig In RUN mode, ON (default), OFF toggles error indications and failure outputs for all errors found during setup.

Exit Required to exit CAL mode, or to exit any Set command writing a value to the module's EEPROM in RUN mode.

S In CAL mode, sets the module's full scale output point at the LVDT core’s maximum position and is the same as pressing FULL SCALE pushbutton. Occasionally it may require setting a second time after using the Z command.

Help Shows all ASCII user commands available for execution over the RS-485 bus, including a few not shown in this list.

LEDs In RUN and CAL modes, outputs the status of the 3 green LEDs, displayed in S-E-P order, e.g.: - * 0 means S LED is off, E LED is flashing slow, and P LED is on. + is a fast flash and ! indicates alternating solid and flashing.

See S2A Manual for further information:

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