Curve Related Commands

The Model 346 supports a variety of temperature sensor types and associated calibration curves to convert the raw sensor readings of ohms and volts into temperature readings that can be used for display and control. From the front panel, users can configure their sensors in one click by selecting a curve from the list of loaded curves and the instrument will automatically configure the input to match. On the remote interface, the user must first configure their input using the INTYPE command. At that point, a curve that matches the configured sensor type can be assigned to the input using the INCRV command. When configuring in this way, non-matching curves are rejected. An example of this is being unable to assign a diode curve to an input configured as an NTC resistor.

When selecting curves, a number of the fields in the curve header are used to help identify the curve. The name is displayed on the front panel for selection, and the format field is used to determine if the curve is valid for a given sensor type. Once the curve is selected, the setpoint limit is used to prevent control outside of a given upper limit.

Once the curve is applied, the breakpoint table is used to convert the raw sensor reading into a temperature reading using linear interpolation between the two nearest points. If the sensor reading is outside of the range of the curve, the instrument will extrapolate using the two nearest points up to a maximum of 50% lower than the lowest point or 5% higher than the highest point. When in this state, a chip is displayed on the input card on the front panel, and the extrapolated bit is set in RDGST?.

Standard curves (1 to 20) are provided for common sensor types and cannot be modified. They are as follows:

Curve ID	Type	Name
2	Diode	DT-670
6	PTC	PT-100
8	NTC	RX-102A-AA
9	NTC	RX-202A-AA
10	NTC	RX-103A-AA
12	Thermocouple	Type K
13	Thermocouple	Type E

User curves, numbered 21 to 60, can be loaded in using the ColdSync tool provided by Lake Shore. User curves must have at least two non-zero points to be valid. Once loaded, user curves can be deleted using the CRVDEL command.

CRVHDR Curve Header Command

CRVHDR <curve>, <name>, <serial num>, <format>, <limit value>, <coeff> [term]

Parameters

Name	Type	Description
curve	nn	Specifies a user curve to configure. Valid entries: 21 to 60.
name	s[32]	The name of the curve. Limited to 32 characters.
serial num	s[16]	The serial number of the curve. Limited to 16 characters.
format	n	The format of the curve. 1 = mV/K 2 = V/K 3 = Ω/K 4 = log Ω/K
limit value	+nnn.nnn	The setpoint limit of the curve in Kelvin.
coeff	nn	The coefficient of the curve. 1 = negative 2 = positive

Example

CRVHDR 21,"DT-670","00011134",2,325.0,1[term]

configures user curve 21 with a name of DT- 670, serial number of 00011134, data format of V/K, setpoint limit of 325 K, and negative temperature coefficient.

Remarks

The coefficient parameter will be calculated automatically based on the first 2 curve datapoints. It is included as a parameter for compatibility with the CRVHDR? query. All parameter fields must be filled with a value. If the sensor does not have a serial number, it is still recommended to enter a non-empty string in this field. The format parameter is a function of sensor type. For example, diodes are V/K, platinums are Ω/K, Cernox are log Ω/K, and thermocouples are mV/K. This sensor format parameter is what’s used to group the curves on the front panel curve selection screen.

CRVHDR? Curve Header Query

CRVHDR? <curve> [term]

Parameters

Name	Type	Description
curve	nn	Specifies a curve header to query. Valid entries: 1–60.

Returns

<name>, <serial num>, <format>, <limit value>, <coeff> [term] (see command for description)

CRVPT Curve Data Point Command

CRVPT <curve>, <index>, <units value>, <temp value>[term]

Parameters

Name	Type	Description
curve	nn	Specifies a user curve to configure. Valid entries: 21 to 60.
index	nnn	The index of the data point. Valid entries: 1 to 200.
units value	+/-nnnnnn	Specifies sensor units for this point to 6 digits.
temp value	+nnnnnn	Specifies the corresponding temperature in kelvin for this point to 6 digits.

Example

CRVPT 21,4,0.13650,479.500,N[term]

sets user curve 21 fourth data point to 0.13650 sensor units and 479.500 K

Remarks

If a sensor reading is measured beyond the last point, or below the first point, the instrument will extrapolate the curve. An extrapolated chip will be present on the front panel, and the extrapolated bit will be set in RDGST?. This extrapolation extends to 50% of the lowest point and 5% above the highest point. For example, if the lowest point is 4 K, the extrapolated range would extend down to 2 K.

CRVPT? Curve Data Point Query

CRVPT? <curve>, <index> [term]

Parameters

Name	Type	Description
curve	nn	Specifies a curve to query. Valid entries: 1 to 60.
index	nnn	The index of the data point. Valid entries: 1 to 200.

Returns

<units value>, <temp value> [term] (see command for description)

INCRV Input Curve Number Command

INCRV <input>, <curve number>[term]

Parameters

Name

Type

Description

input

a

Specifies input to query: A, B, C1, C2, C3, C4, D1, D2, D3, D4, E1, E2, E3, E4, F1, F2, F3, F4, G1, G2, G3, G4, H1, H2, H3, H4

curve number

nn

Specifies which curve a given input uses. If specified curve type does not match the configured input type, the curve number. Defaults to 0. Valid entries:

0 = none

1 to 20 = standard curves

21 to 60 = user curves

Example

INCRV A,23[term]

specifies that input A uses user curve 23 for temperature conversion.

Remarks

If a curve is not assigned to an input, control and display will be in sensor units. When a curve is assigned to an input, control and display readings change to be in temperature units. If the sensor type in the curve header does not match the configured input type, the command is rejected and the curve number returns to 0 (none).

INCRV? Input Curve Number Query

INCRV? <input> [term]

Parameters

Name	Type	Description
input	a	Specifies input to query: A, B, C1, C2, C3, C4, D1, D2, D3, D4, E1, E2, E3, E4, F1, F2, F3, F4, G1, G2, G3, G4, H1, H2, H3, H4

Returns

<curve number> [term] (see command for description)

CRVDEL Curve Delete Command

CRVDEL <curve> [term]

Parameters

Name	Type	Description
curve	nn	The curve number to delete. Must be between 21 and 60.

Example

CRVDEL 21[term] deletes curve 21 from the instrument.

CRVNUMPTS? Input Curve Number of Points Query

CRVNUMPTS? <curve> [term]

Parameters

Name	Type	Description
curve	nn	Specifies the curve to query. Valid entries: 1 to 60.

Remarks

Returns the number of breakpoints defined in the specified curve before encountering a 0K reading, if the curve is empty this will return 0.