• Type
    640B Absolute Pressure Controller
  • Pressure Range
    10, 100, 1000 mmHg (Torr), 60, 100 psi (Full Scale)
  • Fitting Type
    4 VCR, 8 VCR, 0.25 in. Tube, or Surface Mount
  • Flow Rate
    50, 200, 1000, 5000, 10000, 20000, 50000 sccm (nominal Full Scale flow rates for N2 with 15 psig on inlet and atmosphere on outlet)
  • Trip Points
    Two open-collector transistors
    Rated: 250 mA @ 30 VDC
    Adjustable: 1 to 100% of Full Scale
    Hysteresis: 3% of Full Scale
    Indicators: Green LED's on when actuated
  • Pressure Control Accuracy
    ±0.2% of Full Scale
  • Transducer Over Pressure Limit
    45 psia or 2x Full Scale, whichever is greater
  • Maximum Differential Pressure
    30 psi for 20,000 and 50,000 sccm orifices
    150 psi for 50 to 10,000 sccm orifices
    (consistent with transducer overpressure limit)
  • Control Mode
    Downstream standard; Upstream optional
  • Pressure Measurement Accuracy
    ±0.5% of Reading (includes linearity, hysteresis, and repeatability)
  • Zero Temperature Coefficient
    Zero: ±0.02% of Full Scale/°C
  • Span Temperature Coefficient
    Span: ±0.04% of Reading/°C
  • Control Range
    >2 to 100% of Full Scale
  • Typical Response Time
    <1.0 sec (excluding system time constant)
  • Operating Temperature
    0 - 50°C (32° to 122°F)
  • Storage Temperature
    -20 to 80°C (-4° to 176°F)
  • External Leak Integrity
    <10-9 scc/sec He
  • Leak Integrity Through Closed Valve
    Elastomer valve: <10-4 scc/sec He
    Metal valve: <1% of Full Scale (N2 @ 1 atm. ΔP)
    Kel-F valve: <0.5% of Full Scale (N2 @ 1 atm. ΔP)
    (through closed valve)*
  • Wetted Materials
    Standard: 316L S.S., 316L/VAR S.S., Inconel, Nickel
    Optional: Viton®, Kalrez®, Kel-F®
  • Power Required
    ±15 VDC ±5%, 200 mA maximum
  • Connector-Interface
    15-pin male type "D"
  • Meter Response Time
    <100 msec
  • RFI Sensitivity
    SAMA 33.1, 1-abc: <0.2% of Full Scale
  • Input-Output Signals
    0-5 VDC standard; 0-10 VDC optional
  • Cable Length
    100 feet (30 m) maximum
  • Weight
    2.54 lbs. (1.15 kg)
  • Dimensions
    1.5 inches (38.1 mm) x 4.88 inches (124 mm) (4 VCR) x 5.50 inches (140 mm) maximum
  • Compliance


Index Number

The flow through any orifice depends on the size of the orifice, the inlet and outlet pressures, and gas density. To simplify 640/641 orifice selection, use the following procedure:

  1. On the Index Number Table in the figure, choose your inlet pressure from the column of pressures on the left – the pressure that will be applied to the inlet of your 640/641. (Note that the values are absolute pressure.)
  2. Next, from the row of pressures at the top of that table, select your differential (delta) pressure – this is the inlet pressure minus your outlet pressure.
  3. Locate the Index Number – where your selected row and column intersect.
  4. Calculate the Density Correction Factor.

Index Number Table

Maximum Flow Rate

  1. Go to the Orifice Selection Graph (see Figure) and locate your Index Number along the bottom axis.
  2. Draw a vertical line at your Index Number. This line will intersect with the Maximum Flow Rate lines for the valve orifices available.
  3. Choose the orifice whose maximum flow rate exceeds your requirements. If the point on the graph falls close to the maximum flow rate for an orifice, you may choose the next largest orifice number

Orifice Selection Graph

Pressure Range

In the 640 Controller, the Baratron pressure transducer measures absolute pressure; in the 641 model, it measures gauge pressure (pressure relative to ambient barometric pressure). In both models, Full Scale ranges of 10, 100, or 1000 Torr, or 60 or 100 psi are available. Each 640/641 can control pressure from Full Scale to less than 2% of Full Scale. Prudent design suggests choosing the lowest possible Full Scale for the application, taking into consideration the overpressure to which the sensor may be exposed (both normal and accidental).


You want to control a vacuum process at a pressure of 0.5 psia, with a flow rate of 2000 sccm of He. Your inlet pressure is 15 psia, giving a differential pressure (delta P) of 15 psi, resulting in an uncorrected Index Number value of 90. The gas density correction for He is calculated as shown above. Multiplying 2.6 by 90 gives a density-corrected Index Number of 234. Drawing a vertical line on the Orifice Selection Chart at 234 indicates Orifice #3 would be the best choice.

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