SDM-SW8A 8 Channel Switch Closure Module Revision: 7/07 C o p y r i g h t © 1 9 8 7 - 2 0 0 7 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The SDM-SW8A SWITCH CLOSURE INPUT MODULE is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
SDM-SW8A Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. Function........................................................................1 2. Specifications ..............................................................2 3. Power Supply Considerations ....................................3 4. Connections .................................................................4 4.
SDM-SW8A Table of Contents List of Tables 1. 2. 3. 4. 5. Datalogger to SDM-SW8A Connections................................................... 2 SDM-SW8A to SDM-SW8A Connections................................................ 3 Address Jumpers ........................................................................................ 5 Measurement Jumpers................................................................................ 6 Instruction 102 – SDM-SW8A ..............................................
SDM-SW8A Switch Closure Input Module 1. Function The 8 channel SDM-SW8A Switch Closure Input Module (see Figure 1) measures up to 8 channels of switch closure or voltage pulse inputs. Each channel may be configured to read single-pole double-throw (SPDT) switch closure, single-pole single-throw (SPST) switch closure, or voltage pulse. Output options include counts, duty cycle, and state.
SDM-SW8A Switch Closure Input Module 2. Specifications Operating voltage: Current drain: Environmental: 12 VDC nominal (9.6 to 16) 3 mA quiescent, 6 mA active (max) -25 to +50oC, 0 to 90% RH, noncondensing Measurement types: Switch closure (SPDT, SPST) DC voltage pulse Input voltage threshold: From below 0.9 to above 4.
SDM-SW8A Switch Closure Input Module TABLE 2.
SDM-SW8A Switch Closure Input Module 4. Connections All connections to the datalogger, power supply, and other SW8As are made from terminals located under "TO DATALOGGER" on the SW8A (refer to Figure 1). Sensor connections are made at the remaining terminals. 4.1 Connections to Dataloggers and Other SW8As Connections between an SW8A and the CR10 and 21X dataloggers are shown in Table 1. Connections to multiple SW8As are shown in Table 2. CAUTION 1. The order in which connections are made is critical.
SDM-SW8A Switch Closure Input Module TABLE 3. Address Jumpers Pins Address 1-8 2-7 3-6 4-5 00 c c c c 01 c c c nc 02 c c nc c 03 c c nc nc 10 c nc c c 11 c nc c nc 12 c nc nc c 13 c nc nc nc 20 nc c c c 21 nc c c nc 22 nc c nc c 23 nc c nc nc 30 nc nc c c 31 nc nc c nc 32 nc nc nc c 33 nc nc nc nc c = connected nc = not connected FIGURE 2.
SDM-SW8A Switch Closure Input Module 5.2 Measurement Jumpers Near each input channel is a jumper triplet used to configure the channel for the measurement type. The SDM-SW8A is shipped from the factory with each channel configured for DC Voltage pulse. An example of each configuration is illustrated in Figure 2. Table 4 shows jumper pins and the corresponding measurement type. TABLE 4. Measurement Jumpers Measurement Type Pins Jumpered SPDT Switch Closure 1 and 6 SPST Switch Cl. or Open Coll.
SDM-SW8A Switch Closure Input Module Parameter & Data Type FunctOp Constant StartChan Constant Mult, Offset Constant, Variable, Array, or Expression Enter The FunctOp is used to determine the result that will be returned by the SW8A. Numeric Function Code 0 Returns the state of the signal at the time the instruction is executed. A 0 is stored for low and a 1 is stored for high. 1 Returns the duty cycle of the signal. The result is the percentage of time the signal is high during the scan interval.
SDM-SW8A Switch Closure Input Module NOTE Instruction 102 is not contained in all CR10 or 21X PROMS. To verify that the datalogger contains the Instruction, enter 102 into a datalogger Programming Table. If the Instruction is accepted, the PROM contains the Instruction. Repetitions (Reps, Parameter 1) specifies the number of SW8A channels to read. Parameter 2 is the address of the first SW8A.
SDM-SW8A Switch Closure Input Module 7. Datalogger Program Details 7.1 Datalogger Scan Rate The Module samples channel state every 2 ms and accumulates the information for duty cycle and counts. Each channel has one 16 bit accumulator for duty cycle and one for counts. The accumulators are reset when the datalogger requests information from the SW8A and when the count exceeds 65535. The datalogger scan rate must be frequent enough to avoid SW8A accumulator overflow.
SDM-SW8A Switch Closure Input Module forces a watchdog reset by addressing the Module and requesting sufficient information to cause a minimum of 65 clock line transitions. Advantages to the trapping routine are: • The bombed processor is detected before erroneous values (-99999) are included in subsequent processing. • The processor may be reset sooner. • The time of processor failure may be logged by the datalogger. • Number of failures may be logged.
SDM-SW8A Switch Closure Input Module 8.2 SPST Switch Closure Single-pole single-throw switches are either open (high state) or connected to ground (low state). Typical SPST switches include contact closure (reed switch) anemometers, tipping bucket rain gauges, and open collectors (semiconductor switches). Many control devices utilize open collectors and provide terminals for monitoring the switch.
SDM-SW8A Switch Closure Input Module 50% Duty Cycle - The "worst case" duty cycle measurement error for a 50% duty cycle at a given input frequency is ±ERROR = Hz * 0.4 where ERROR = Actual Duty Cycle ±Measured Duty Cycle. For example, a 50% duty cycle at 10 Hz could be measured as 46% to 54% in the worst case. Minimum/Maximum - The measurable minimum/maximum duty cycle is defined by the 5 ms pulse width specification of the SW8A.
SDM-SW8A Switch Closure Input Module addressed SW8A is present. The 21X works similarly, except the data from the SW8A is input to single ended analog channel 1, not C1. Depending on the Command, Reps, and Channel information, the module will shift out one or more bytes to the datalogger, again using C2 as a clock driven by the datalogger. The module shifts out each bit on the falling edge of the clock; the datalogger reads each bit on the rising edge of the clock.
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Appendix A. Program Example The Edlog program is an example only and is not meant to be used verbatim. In application, the concepts illustrated here are likely to be only fragments of a larger program. The example program reads all 8 ports of an SW8A which is set to address 00. It is read three times per scan, once each for State, Duty Cycle, and Count information. The scan rate is fixed at 1 second, with a 5 minute output of State, average Duty Cycle, and average Count.
Appendix A. Program Example FIGURE A-1. Example Program Flow Chart PROGRAM EXAMPLE Input Locations Used: 1:STATE #1 13:DUTY #5 2:STATE #2 14:DUTY #6 3:STATE #3 15:DUTY #7 4:STATE #4 16:DUTY #8 5:STATE #5 17:COUNT#1 6:STATE #6 18:COUNT #2 7:STATE #7 19:COUNT #3 8:STATE #8 20:COUNT #4 9:DUTY #1 21:COUNT #5 10:DUTY #2 22:COUNT #6 11:DUTY #3 23:COUNT #7 12:DUTY #4 24:COUNT #8 25:RESET CNT Output Arrays: ID = 105, 27 ELEMENTS ID = 112, 4 ELEMENTS 105, DAY, HRMN, STATE #1,... STATE #8, DUTY #1, ...
Appendix A. Program Example *Table 1 Programs 01: 1 Sec. execution interval 1: Do (P86) 1: 1 Call Subroutine 1 If SDM-SW8A was just programmed or its processor is bombed, set intermediate processing disable flag. 2: 1 If Flag/Port (P9) 1: 21 Do if flag 1 is low 2: 19 Set high Flag 9 3: If X<=>F (P89) 1: 1 2: 4 3: 0 4: 19 X Loc state #1 < F Set high Flag 9 OUTPUT STATE AND AVERAGE DUTY CYCLE EVERY 5 MINUTES.
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