M P B CONTROL RELAYS REVERSING BIASING RELAY RELAY M M P B P B Reversing relays increase their branch signal in response to a decrease in their pilot signal. Most have a 1:1 relationship. Johnson Controls made a reversing relay with a 1:2 relationship. The branch pressure can be biased for sequencing purposes. Biasing relays increase their branch signal in relationship to the pilot signal. The branch signal may be off set to a different pressure than the pilot signal. The branch may increase at ratios of 1:1, 1:2, 1:3.33 or 1:5. RATIO RELAY P TURNDOWN RATIO RELAY (KREUTER) M B Ratio relays increase their branch signal at a fixed ratio relative to their pilot signal. The ratios are 1:2, 1:4, 1:6. Reducing ratio relays decrease the branch signal relative to the pilot signals. The output signal cannot be biased with these relays. The turndown ratio relay allows the branch signal to be biased relative to the pilot signal. The branch signal may reduced at a selectable ratio via a dial on the relay. 2.13 GRADUAL SWITCH Gradual switches can be one or two pipe. They can be used as a minimum positioner as the PRV on page 2.12. They are very useful in simulating transmission signals while calibrating receiver controllers.
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