CCST 44 — Loop Current vs Process Variable Check

Briefing

During a loop check, the technician simulates a process value at the transmitter with a calibrator and reads the loop current at the PLC. SIM_PCT is the simulated value, 0 to 100 percent of range. MEASURED_MA_X100 is the current the PLC sees, in hundredths of a milliamp (400 = 4.00 mA). Build the check table row: - EXPECTED_MA_X100: the current a healthy loop should carry for that percent. The signal runs 4-20 mA, so 0 percent is 4.00 mA and 100 percent is 20.00 mA. - POINT_PASS: the measured current is within +/-1 percent of span (+/-0.16 mA, which is 16) of the expected current. The limit includes its edge. - POINT_FAIL: the measured current is outside that band. Exactly one of POINT_PASS and POINT_FAIL is on. A comparison cannot be written against a negative number, such as | (A > -5) |. To test a negative reading, flip its sign first with SUB(0, X) and compare the flipped value with a positive limit. Maths is built with Math boxes (ADD, SUB and MUL), or in the Code tab one assignment per line. Comparisons are built with Compare boxes, or in the Code tab as contacts, for example | (A > B) | := LAMP ;

Objectives

• EXPECTED_MA_X100 follows the simulated percent: 400 at 0, 800 at 25, 2000 at 100
• A measurement within +/-0.16 mA of expected passes, high or low, edge included
• A measurement outside the band, including a dead 0 mA loop, fails

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #10 percent, 4.02 mA → pass

   A small error passes

2. #225 percent, 8.00 mA → pass

   An exact reading passes

3. #350 percent, 11.90 mA → pass

   A low reading inside the band passes

4. #475 percent, 16.40 mA → fail

   A high reading outside the band fails

5. #5100 percent: 19.84 passes, 19.83 fails

   The band edge is inside the band

6. #60 percent, 0.00 mA → fail

   A dead loop is not a zero reading

7. #710 percent → expects 5.60 mA

   The expected value follows the simulated percent