# FC 8 - Rate Limiter

The output of this block equals the input until the input rate of change exceeds the limit value (S3 and S4). When the rate of change of the input is greater than the limit, the output changes at the rate established by the limit until the output equals the input. Outputs:

 Blk Type Description N R Output rate equals input rate until the input rate exceeds the rate limit. Then, the output rate equals the limit.

Specifications:

 Spec Tune Default Type Range Description S1 N 5 I Note 1 Block address of input S2 N 0 I Note 1 Block address of track switch signal: 0 = track 1 = release S3 Y 0.000 R Full Increase rate limit (1 / sec) S4 Y 0.000 R Full Decrease rate limit (1 / sec)

NOTES:

1. Maximum values are: 9,998 for the BRC-100, IMMFP11/12 and 31,998 for the HAC

8.1 Explanation

Function code 8 limits the rate of change of the output according to preset limits. To activate this function set <S2> to a logic 1. With <S2> set to a logic 0, the output is the same as the input.

Specification S3 is the rate limit of an increasing input signal in engineering units per second. As long as the input rate of increase is less than S3, the output equals the input. When the rate at which the input increases exceeds the setting of S3, the output changes at the rate set by S3 as long as the input rate of increase remains greater. Specification S4 limits the output rate of decrease when the input rate of decrease is greater than S4.

8.2 Applications

Figure 8-1 illustrates how to use the rate limiter for bumpless transfer. In the example, the M/A station sends an automatic (logic 1) or manual (logic 0) signal to <S2> of the rate limiter. When in automatic, function code 8 limits the rate of change to the set point. For example, placing the station in automatic may cause a drastic change in set point demand. The rate limiter slows the increase or decrease set point demand to the station providing a bumpless transfer from manual to automatic. 