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CBLUSB01 数据表(PDF) 28 Page - Red Lion Controls. Inc |
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CBLUSB01 数据表(HTML) 28 Page - Red Lion Controls. Inc |
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28 / 36 page ![]() 28 Communication Format Data is transferred from the meter through a serial communication channel. In serial communications, the voltage is switched between a high and low level at a predetermined rate (baud rate) using ASCII encoding. The receiving device reads the voltage levels at the same intervals and then translates the switched levels back to a character. The voltage level conventions depend on the interface standard. The table lists the voltage levels for each standard. Data is transmitted one byte at a time with a variable idle period between characters (0 to ∞). Each ASCII character is “framed” with a beginning start bit, an optional error detection parity bit and one or more ending stop bits. The data format and baud rate must match that of other equipment in order for communication to take place. The figures list the data formats employed by the meter. Start bit and Data bits Data transmission always begins with the start bit. The start bit signals the receiving device to prepare for reception of data. One bit period later, the least significant bit of the ASCII encoded character is transmitted, followed by the remaining data bits. The receiving device then reads each bit position as they are transmitted. Since the sending and receiving devices operate at the same transmission speed (baud rate), the data is read without timing errors. Parity bit After the data bits, the parity bit is sent. The transmitter sets the parity bit to a zero or a one, so that the total number of ones contained in the transmission (including the parity bit) is either even or odd. This bit is used by the receiver to detect errors that may occur to an odd number of bits in the transmission. However, a single parity bit cannot detect errors that may occur to an even number of bits. Given this limitation, the parity bit is often ignored by the receiving device. The PAX meter ignores the parity bit of incoming data and sets the parity bit to odd, even or none (mark parity) for outgoing data. Stop bit The last character transmitted is the stop bit. The stop bit provides a single bit period pause to allow the receiver to prepare to re-synchronize to the start of a new transmission (start bit of next byte). The receiver then continuously looks for the occurrence of the start bit. IDLE 0 b01 b 2 bb3 b4 b56 b 1 IDLE IDLE IDLE 0 b b 0 b 13 2 bb4 b5 b6 P1 IDLE IDLE 0 b bb 01 b b3 24 b b56 11 (7 data, no parity, 2 stop) (7 data, parity, 1 stop) (8 data, no parity, 1 stop) Start bit Stop bit Note: b - b is ASCII data. 0 7 7 b Character Frame Figure LOGIC RS232* RS485* INTERFACE STATE 1 TXD,RXD; -3 to -15 V a-b < -200 mV mark (idle) 0 TXD,RXD; +3 to +15 V a-b > +200 mV space (active) * Voltage levels at the Receiver 8-Out ASIN Analog Type tYPE AN-LO AN-HI udt Analog Update Time PAR Analog Assignment Analog Low Scale Value Analog High Scale Value Pro Burn-out Action burn PAXT ONLY 6.8 mOdUle 8 - analOg OUTpUT parameTers () Ñ PARAMETER MENU Enter the analog output type. For 0-20 mA or 4-20 mA use terminals 18 and 19. For 0-10 V use terminals 16 and 17. Only one range can be used at a time. ANALOG TYPE ANALOG ASSIGNMENT SELECTION 0 to 10 V 4 to 20 mA 0 to 20 mA RANGE Enter the Display Value that corresponds to 0 mA (0-20 mA) , 4 mA (4-20 mA) or 0 VDC (0-10 VDC). ANALOG LOW SCALE VALUE ANALOG HIGH SCALE VALUE ANALOG UPDATE TIME PROBE BURN-OUT ACTION (PAXT ONLY) to to to Enter the source for the analog output to retransmit: = Display Input Value = Maximum Display Input Value = Minimum Display Input Value = Totalize Display Value Enter the Display Value that corresponds to 20 mA (0-20 mA) , 20 mA (4-20 mA) or 10 VDC (0-10 VDC). Enter the analog output update rate in seconds. A value of 0.0 allows the meter to update the analog output at a rate of 20/sec. Enter the probe burn-out action. In the event of a temperature probe failure, the analog output can be programmed for low or high scale. Ñ - An analog output card must be installed in order to access this module. |
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