Honeywell HC900 Reference Guide

Function Blocks
FI Frequency Input
160 HC900 Hybrid Control Designer Function Block Reference Guide Revision 11
2/07
Example
Say you configure the block as follows.
Pulse Width (Range) = 500µsec (10Hz-500Hz)
Frequency Span Low = 50Hz
Frequency Span High = 450Hz
Output range in EU = 0 - 100
Bias = 8
Failsafe = Upscale (upper output range)
Assume the module is receiving a 255Hz signal, including noise. Assume 2% of pulses are noise, that is,
are less than the minimum pulse width 500 µsec. The block rejects this 2% and does not count them in the
frequency. The remaining 98% valid pulses are counted, which is an effective signal of 250Hz. From the
output equation above,
OUT = [(250–50) / (450-50)] * (100 – 0) + 0 + 8
= [200/400] * 100 + 8
= 0.5 * 100 + 8
= 50 + 8
= 58 EU
If the frequency of the effective signal (>500 µsec pulse width) changes to outside the specified range of
10-500Hz, a failure-to-convert error occurs and the output goes to failsafe, in this case upscale (100).

Honeywell HC900 Specifications

General

Series	HC900
Redundancy	Optional
Programming Language	Function Block Diagram, Ladder Logic, Structured Text
Inputs	Analog, Digital
Outputs	Analog, Digital, Relay
Display	Optional
Control	PID, Advanced Control
Power Supply	24V DC or 100-240V AC
Storage Temperature	-40°C to 85°C
Humidity	5% to 95% non-condensing
Communication Protocols	Modbus, Ethernet