TM Interface Manual Continuous Level Controls 7100 ™ Leak Detect Stik Magnetostrictive Level System ABSOLUTE PROCESS CONTROL KNOW WHERE YOU ARE...
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Contents Chapter 1: Description of Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Data Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Frame Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Installation and Dimension Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1: Description of Probe The 7100 liquid level probe uses a proprietary data transmission technique providing a compact information format for level and temperature data, and a signal pattern which is very easily recognizable at the console. 1.1: Data Protocol Transmission consists of a sequence of similarly formatted frames of data, each frame in turn, consisting of 15 pulse pairs and a pause period.
Return to Start of Frame High Ref Product Low Ref Product #9 #10 #11 #12 #13 #14 #15 #16 Product Temp #2 #8 Circuit Temp Water #7 Product Temp #1 #6 Temp #5 #5 Product #4 Temp #4 #3 Product #2 Temp #3 #1 Pause 16 Time Slots Figure 1: One frame of Data 1.2: Frame Protocol All 7100 probes transmit data in the same general format. In this format, information is conveyed during a discrete period of time called a frame. The duration of a frame varies depending on the probe type.
The type of information contained in each reading varies depending on the probe type. Table 2 specifies the data pattern for various probe types.
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6 7100 Dimension Drawing, Page 1
7 7100 Dimension Drawing, Page 2
Chapter 2: Interfacing to Probe The pulse signals coming from the probe are superimposed onto the nominal 24 VDC power supply connections. As shown in Figure 3, the pulses are negative-going and are large in amplitude, nominally 20 volts peak. The peak is negative going and only a few microseconds in duration. The leading edge is the proper edge to use for timing purposes. The large signal amplitude offers high noise immunity.
4.5mS Reset 4.5mS Watchdog Reset Watchdog ts-s Figure 4: Start Pulse NOTE 1: ts-s = time from 1st start pulse in one frame to next start pulse in the next frame. NOTE 2: Start pulse can start anywhere in the 4.5 ms frame. The stop pulse will follow at the correct time. The ts-s is not consistent. The user does not have the 4.5 ms frame as a reference. The user must use the watchdog timeout during the pause frame to “sync up”. The watchdog timer should be reset on both the start and stop pulse. 4.
2.1: Interface Hardware A typical console has the following sub-systems: 1. Probe Mulitplexer 2. Intrinsic Safety Barrier 3. Pulse Discriminator 4. Gate Circuit 5. High Speed Counter Comparator Threshold Use leading edges of comparator output to start and stop counters. Comparator Output Gate Signal for Counters Figure 6: Start and Stop Counters Figure 7 shows typical means of achieving each of these sub-systems. The multiplexing is achieved with the use of a PNP-style bipolar driver IC.
2981 or Equivalent (PNP Driver I.C.) VCC 49.9K Metal Film 5 Volt Logic Probe Select Lines (only one line is active at a time.) 8 Probe Connections GND s VCC 0.1 uF. 5:1 Pulse Transformer GND 150 +24 VDC 1 mH. Return signals are coupled through the VCC Pin and the 150 Ohm barrier resistor and coupling capacitor to the step-up pulse transformer. The inductor passes the 24 Volts without shorting the return pulse.
Chapter 3: Getting the Data The method that data is communicated between the probe and the console is described in Section 1.1: Data Protocol. The user should understand the data protocol scheme before attempting to process the data. 3.1: Synchronizing with a Watchdog Timer Referring to Figures 1 and 5, note that there is only one pause period per frame and therefore, only one time during the sequence when no pulses will be received for approximately 9 milliseconds.
3.3: System Software Setup Although one frame of data is sufficient to obtain valid product, water, and temperature readings, averaging multiple frames is generally much more appropriate. This is because all elements in the system are subject to slight uncertainties and/or the effects of electrical noise or mechanical vibration. This includes the magnetostrictive wire in the probe, the probe electronics, the transmission wire between the probe and the console, and the console electronics.
Chapter 4: Processing the Data Data acquisition was discussed in Section 3 to the degree that memory locations are filled with an array of data from a selected number of frames. It is now appropriate to test for data integrity, average and/or filter the data, and then convert from binary counter values to scaled, meaningful numbers. 4.1: Front End Algorithm A technique for eliminating any possible erroneous data is to discard some of the highest and lowest count values.
Chapter 5: Computing the Temperature A probe reading contains 15 values for product, water and temperature. The product and water values are each useful by themselves (a single product or water value may be converted with linear math to represent the float position). Unlike the product and water values, the temperature values are always accompanied by two reference values. A single temperature sensor value is of no use without its associated reference temperature values.
Step 3 - Using the attached table, find the linear temperature interval (TLIN1, TLIN2) and then the actual temperature interval (T1, T2) for TLIN. Example. TLIN = 15.763 °C, TLIN1 = 15.178 °C, TLIN2 = 16.321 °C, T1 = 14 °C, T2 = 15 °C. Step 4 - Calculate accurate table interpolated temperature T, using linear interpolation within intervals (TLIN1, TLIN2) and (T1, T2). T = ((TLIN2 - TLIN1) * T2 - (TLIN2 - TLIN) * (T2 - T1)) / (TLIN2 - TLIN1) Example: TLIN = 15.763 °C, TLIN1 = 15.178 °C, TLIN2 = 16.
Actual Temp °C -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 Linear Temp °C -25.141 -24.884 -24.613 -24.327 -24.030 -23.714 -23.386 -23.038 -22.678 -22.297 -21.900 -21.488 -21.055 -20.601 -20.133 -19.641 -19.126 -18.598 -18.042 -17.466 -16.871 -16.249 -15.611 -14.945 -14.258 -13.554 -12.823 -12.068 -11.291 -10.497 -9.671 -8.832 -7.968 -7.078 -6.178 -5.252 -4.297 -3.332 -2.347 -1.
EC Declaration of Conformity AMETEK Automation & Process Technologies 6380 Brockway Road, Peck, MI 48466 USA Manufacturer: Identification of Equipment: 7100 Stik Series Liquid Level Transducer Description of Device: The device is a permanently mounted liquid level probe. It determines the level of a liquid based on signal reflections, caused by magnetic floats, in a wire running the length of the probe.
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