MI 011-476
–
January 1980 Principle of Operation
2
Standard Specifications
Principle of Operation
1. A differential linkage measures difference between measurement pointer and setting
index positions. This error signal moves proportioning lever.
2. Proportioning lever pivots at its center on end of a flat spring.
3. This motion changes flapper nozzle relationship, causing relay to establish an output
pressure.
4. Output pressure is fed back to proportioning bellows, which acts through
proportioning lever to rebalance flapper nozzle.
5. Reset bellows and tank assembly are used when measurement must be maintained
exactly at control point (without “offset”).
6. Derivative tank assembly is used to improve system response to a slow process.
Types of Control
Suffix Code –A1:
A2:
A3:
A4:
A5:
A7:
A8:
On-Off
Proportional
Proportional plus Derivative
Proportional plus Reset
Proportional plus Reset plus Derivative
Differential Gap
Automatic Shutdown
Control Limits
Proportional:
Reset:
Derivative:
Differential Gap:
4 to 400%
0.01 to 50 minutes per repeat
0.05 to 50 minutes
1 to 100%
Output Signal:
Air Supply:
Air Consumption:
Air Connections:
Ambient Temperature Limits:
Weight:
Case:
3-15 psi or 20-100 kPa
20 psi (140 kPa)
0.3 std ft
3
/min (0.5 std m
3
/h)
Tapped for 1/4 NPT
–40 to +180°F (–40 to +80°C)
Approx. 10 lb (4.5 kg), excluding element
Glass fiber reinforced plastic
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