401-405 SERIES - 1 -
1. General Information
1. General Information
1.1. Overview
1.1.1. 400 Series Family
The Hastings 400 Series is a family of flow instruments which is specifically designed to meet the needs
of the industrial gas flow market. The “I” family in the 400 Series features an IP-65 enclosure which
allows the use of the instrument in a wide variety of environments. The 400 I products consist of four
configurations: a flow meter, HFM-I-401, which has a nominal nitrogen full scale between 10 SLM and
300 SLM and a corresponding flow controller, the HFC-I-403; a larger flow meter, HFM-I-405, which
ranges from 100 SLM to 2500 SLM, and a corresponding flow controller, the HFC-I-407. These
instruments are configured in a convenient in-line flow-through design with standard fittings. Each
instrument in the series can be driven by either a +24 VDC power supply or a bipolar ±15 volt supply.
The electrical connection can be made via either a terminal strip located inside the enclosure or
optionally through an IP-65 compatible electrical connector. Also, these instruments include both
analog and digital communications capabilities.
1.1.2. 400 Series Meters
The Hastings HFM-I-401 and HFM-I-405 thermal mass flow meters are designed to provide very
accurate measurements over a wide range of flow rates and environmental conditions. The design is
such that no damage will occur from moderate overpressure or overflows and no maintenance is
required under normal operating conditions when using clean gases.
1.1.3. Measurement Approach
The instrument is based on mass flow sensing. This is accomplished by combining a high-speed thermal
transfer sensor with a parallel laminar flow shunt (see Figure 1-1). The flow through the meter is split
between the sensor and shunt in a constant ratio set by the full scale range. The thermal sensor consists
of a stainless steel tube with a heater at its center and two thermocouples symmetrically located
upstream and downstream of the heater. The ends of the sensor tube pass through an aluminum block
and into the stainless steel sensor base. With no flow in the tube the thermocouples report the same
elevated temperature; however a forward flow cools the upstream thermocouple relative to the
downstream. This temperature difference generates a voltage signal in the sensor which is digitized and
transferred to the main processor in the electronics enclosure. The processor uses this real-time
information and the sensor/shunt characteristics stored in non-volatile memory to calculate and report
the flow.
To ensure an inherently linear response to flow, both the thermal sensor and the shunt have been
engineered to overcome problems common to other flow meter designs. For example, nonlinearities and
performance variations often arise in typical flow meters due to pressure-related effects at the entrance
and exit areas of the laminar flow shunt. Hastings has designed the 400 Series meters such that the flow-
critical splitting occurs at locations safely downstream from the entrance effects and well upstream from
the exit effects. This vastly improves the stability of the flow ratio between the sensor and shunt. The
result of this design feature is a better measurement when the specific gravity of the flowing medium
varies, for instance due to changes in pressure or gas type. Also, a common problem in typical flow
meters is a slow response to flow changes. To improve response time, some flow meter designs
introduce impurities such as silica gel. Alternatively, Hastings has designed the 400 Series sensor with
reduced thermal mass to improve the response time without exposing additional materials to the gas
stream.
1.1.4. Additional Functions
These instruments contain a number of functions in addition to reporting flow which include:
• Settable alarms and warnings with semiconductor switch outputs
